TIG Welding Current Chart: Amps by Metal Thickness

A weekend fabricator once spent an entire Saturday destroying 1/8-inch aluminum: the bead sat on top like a worm, the tungsten turned grey, and the puddle never wetted out. The problem wasn’t skill — the machine was set to 60 amps because the chart taped to the cart had been photocopied from a different process, and nobody had re-checked it against the actual thickness in hand.

What a TIG Welding Current Chart Actually Tells You

A TIG welding current chart is a lookup table: you find your base metal, find its thickness, and read back a recommended starting amperage range. That’s the whole promise. A chart for mild steel might say 1/8-inch plate starts somewhere around 80 to 130 amps, and the classic rule of thumb behind nearly every one of those numbers is roughly 1 amp per 0.001 inch (one “thou”) of material thickness. What the chart is really giving you is a first dial position, not a finished setting.

That distinction matters more in TIG than in almost any other process, and it’s worth understanding the physics before you trust a number off a laminated card.

Why Amperage Is the Main Dial

In gas tungsten arc welding, the arc is struck between a non-consumable tungsten electrode and the workpiece. The American Welding Society defines GTAW exactly this way: an arc welding process that uses a tungsten electrode to establish the arc, with shielding gas protecting the puddle and filler metal added separately if needed. Because the electrode doesn’t melt into the joint, the operator controls heat and filler independently, which is both TIG’s greatest strength and its biggest sensitivity.

Amperage is the current flowing through that arc, and it’s the primary lever you have over heat input. More amps means a hotter arc, deeper penetration, and a wider puddle. Fewer amps means a shallower, cooler weld that sits on the surface. But amperage never works alone. True heat input is a function of amperage, arc voltage, travel speed, and process efficiency — which is why current alone never determines penetration. Run the same 90 amps and move twice as fast, and you’ve effectively halved the heat going into the plate.

Four terms show up on every chart and in every discussion of settings:

• Amperage — the current in the arc; the main heat control.
• Arc voltage — largely a function of arc length; a longer arc raises voltage and spreads heat wider.
• Travel speed — how quickly the puddle moves; faster means less heat per inch.
• Heat input — the combined energy actually absorbed by the metal, usually expressed as joules per inch or kilojoules per millimeter.

Why TIG Punishes Wrong Amperage Faster

Stick and MIG are forgiving in ways TIG isn’t. A stick electrode has a heavy flux coating and a large molten pool that hides a lot of sins; MIG delivers wire at a fixed rate that helps carry the arc. In TIG, the arc is concentrated in a tiny area under a precision-pointed tungsten, and the filler rod goes in by hand. There’s no flux to smooth over a cold joint and no wire feeding at a steady rate to keep the puddle fed. Set the machine too cold and the filler sits on top of unfused base metal. Set it too hot and the puddle collapses straight through thin material before your hand can react.

The arc itself also produces visible smoke containing harmful metal fume and gas by-products, as OSHA’s welding fact sheet notes, so getting the heat right isn’t only a quality issue — it limits how much contamination you generate in the first place.

What the Chart Does Not Tell You

Here’s the part most charts leave out, and the reason two welders can read the same row and get different results. A thickness-and-material chart has no idea about:

• Joint design — an inside corner acts as a heat sink and needs more amps; a bare outside corner edge needs far less.
• Welding position — vertical and overhead usually call for 10–15% less current than flat.
• Travel speed — fast travel demands more amps; slow travel demands fewer.
• Fit-up and root gap — a loose gap pulls heat away and raises the requirement.
• Tungsten size and grind — undersized tungsten balls up; oversized tungsten gives an erratic arc at low amps.
• Shielding gas, cup size, and arc length — all of which shift how heat spreads.
• Pulsing and AC balance — modern machine features no static chart can account for.

That’s the goal for everything that follows: learn to read the chart quickly, understand the arithmetic underneath it, then adjust intelligently for the joint actually clamped in front of you. Whether you’re running steel, stainless, or preparing for aluminum cleaning before welding, the reading process is the same — baseline first, then modify for reality.

The Rules of Thumb Behind Every Current Chart

Every TIG amperage chart, whether it is taped to a shop cart or printed in a machine manual, is built on the same small handful of arithmetic rules. Learn those rules and you can estimate a usable setting with a scrap of the part in your hand and no chart at all. That is the real skill the chart is trying to teach you.

The One-Amp-Per-Thou Rule for Mild Steel

The oldest rule in TIG welding is dead simple: use about 1 amp of current for every 0.001 inch (one “thou”) of material thickness as a starting point on mild or carbon steel, butt joint, flat position, clean fit-up. So a 0.100-inch thick piece of carbon steel wants roughly 100 amps to get started, and 0.060-inch (16 gauge) sheet wants about 60.

The metric version of the same idea, which is what most Australian and UK shops run on, is roughly 25 amps per 1 millimetre of thickness. That comes from the fact that 1 mm is about 0.039 inch, which would give 39 amps under the imperial rule. In practice, welders have found that 25 A/mm works better as an everyday number for TIG because it lands in the middle of the useful range rather than at the hot edge. A 3 mm plate therefore starts around 75 amps. Published shop references like the Weldclass rules of thumb guide use this figure, and it lines up closely with what machine manufacturers such as Miller publish in their TIG setting calculators.

Worked Conversions Across Imperial and Metric

Since thickness is quoted both ways depending on whether you are reading a US gauge chart or a metric one, it helps to see the pairs side by side:

Thickness	Metric	1 A/thou baseline	25 A/mm baseline
0.040 in	1.0 mm	~40 A	~25 A
0.063 in (16 ga)	1.6 mm	~63 A	~40 A
0.090 in	2.4 mm	~90 A	~60 A
0.125 in (1/8 in)	3.0 mm	~125 A	~75 A
0.250 in (1/4 in)	6.0 mm	~250 A	~150 A

Notice the two rules do not agree, and that is worth pausing on. The imperial rule runs hot on thick material because heat does not scale linearly with thickness: thicker plate acts as its own heat sink, so doubling thickness does not double the amps you need. The 1 A/thou rule is most accurate from about 0.030 in to 0.120 in. Past roughly 3 mm, most welders quietly slide toward the 25 A/mm figure, which is why a 1/4-inch fillet on a real job rarely runs anywhere near 250 amps and more often sits in the 140 to 180 amp range.

Why Published Charts Give You a Range

Look up 1/8-inch mild steel and you will find charts recommending anywhere from 80 to 130 amps. That spread is not sloppiness. It exists because the chart is quietly assuming a joint and a position for you: flat butt joint, good fit-up, reasonable travel speed. Move the same joint vertical-up and you want less current. Add a 1/32-inch root gap and you want more. Tack-welded parts clamped to a steel fixture pull heat away and want more again. The range is the adjustment for those variables, which we will work through in a later section.

When to Deviate Upward or Downward

The baseline number is your zero point. Adjust it deliberately:

• Go up for root gaps and open fit-up, outside corner joints that lose heat into thin edges, out-of-position welding done quickly, oxidised or dirty surfaces, and parts clamped to a chill block or heavy fixture.
• Go down for inside corner joints that concentrate heat, thick heatsink backing under thin sheet, aluminium where the whole part preheats as you go, and any joint where the part is already warm from earlier tacks.

One material-specific warning before we move on: the steel rules above are only a rough bridge for other metals. Aluminium pulls heat away fast and carries an oxide layer that must be cleaned off in the arc, so it generally wants more current than steel of equal thickness, and stainless holds heat and needs less. If you are working aluminium with a non-TIG process, guides like our aluminium MIG welding guide use different baselines again, which is exactly why a chart photocopied from the wrong process, like the one in our opening story, destroys parts so efficiently.

Reading the Chart by Material: Steel, Stainless, Aluminum, and Exotics

The biggest key to any current chart isn’t thickness alone, it’s thermal conductivity. Some metals pull heat away from the puddle faster than the arc can feed it, while others hold it in. Once you read the chart with that in mind, the jumps in amperage between materials will make a lot more sense.

Mild Steel: The Baseline

Mild steel is the reference point for most TIG amperage charts. Its conductivity falls in the middle, so it’s the easiest to predict. For clean, flat-position welds, the most common starting point is about 1 amp per 0.001 inch of thickness with a quality 2% ceriated or lanthanated electrode. A 0.090-inch bracket may only need around 90 amps, while a quarter-inch plate will often land between 220 and 250 amps once joint fit-up is factored in.

Above all else, steel is forgiving. That margin is exactly why it’s best to dial in your technique on mild steel before moving onto materials that are far less tolerant to excess heat.

Stainless Steel: Hold Less Heat, Run Less Amps

Unlike mild steel, austenitic stainless steel retains heat instead of conducting it away. For that reason, most charts call for about 10 to 20 percent less current than the same thickness of mild steel. For example, a 0.062-inch butt joint that may take 60 amps on steel often only needs 50 to 55 amps on stainless.

This isn’t just for puddle control. Excess heat input can lead to chromium carbide precipitation in the heat-affected zone, a concern that becomes critical for code work. For procedures with little room for error, such as those outlined in Aerospace TIG Welding: Standards, Techniques, and Training, amperage discipline is required, not optional. With stainless, less current paired with faster travel will go a long way towards protecting the alloy.

Aluminum, Copper, and Brass: High Conductivity, High Amps

Aluminum flips the rule completely. With roughly three times the thermal conductivity of carbon steel, it pulls heat away from the arc at a rapid rate. On AC, this typically calls for 1.2 to 1.25 amps per 0.001 inch of thickness, rather than 1.0. Additionally, its tenacious oxide layer must be broken up by the cleaning action of AC before wetting can occur, a topic that will be expanded on in the next section.

Copper takes this to an even greater extreme. Due to its aggressive heat dissipation, charts often call for at least 50 percent more current than steel for equal thickness, and up to double for thicker oxygen-free copper. Brass (a zinc-copper alloy) falls somewhere in between, but still generally demands more amps than steel. For all of these highly conductive metals, prep is just as vital as your settings. Proper degreasing and oxide removal, as detailed in Aluminum Cleaner for Welding: How to Prep Aluminum Right, is non-negotiable to prevent a stubborn, un-wettable puddle.

Titanium, Zirconium, and Nickel Alloys: A Ceiling, Not a Target

For reactive metals and superalloys, the goal is the opposite of maximum heat delivery. Titanium and zirconium are extremely sensitive to atmospheric contamination, often requiring trailing shields or purge dams in addition to your cup. Nickel alloys, such as those covered under Alloy 20 Welding: Procedures, Filler Metals, and Best Practices, are typically welded to a documented procedure with tight heat input limits.

For these materials, treat the chart value as a ceiling. Running slightly under the mild steel figure, keeping a consistent, moving travel speed, and never lingering in one spot is far safer than pushing for extra penetration.

Mass, Fit-Up, and the Root Pass

Charts are based off of clean, flat-position coupons. Real parts rarely are. Thin sheet has little mass to sink heat, making it far easier to blow through than its gauge suggests. Thick plate, on the other hand, acts as a heat sink and may require nudging up from a barebones starting point. The most drastic change comes from tube and pipe root passes. With an open root and almost no backing mass, a setting that works on a flat plate can easily blow the root through. For these joints, dropping below the flat-plate amperage and letting travel speed control penetration is the most reliable approach.

Representative Starting Amperage by Material and Thickness

The ranges below are flat-position starting points for clean, well-fitted material. Treat them as a place to test from, not a final setting.

Thickness	Mild Steel (DCEN)	Stainless (DCEN)	Aluminum (AC)	Copper / Brass
0.040 in (1 mm)	40–50 A	35–45 A	50–65 A	60–85 A
0.062 in (1.6 mm)	60–70 A	50–60 A	75–90 A	90–115 A
0.090 in (2.4 mm)	85–100 A	75–85 A	105–125 A	130–165 A
0.125 in (3.2 mm)	115–130 A	100–115 A	135–160 A	175–210 A
0.188 in (4.8 mm)	170–190 A	150–170 A	190–215 A	240–285 A
0.250 in (6.4 mm)	220–250 A	190–220 A	230–265 A	300 A+

Exact numbers will always vary between charts. For a solid cross-check, Miller’s TIG welding calculator offers material-based suggestions, while SimpleWeld’s amperage chart is a useful way to see the spread across published values. When the two disagree, take the average and fine-tune from there with a test bead.

Aluminum TIG on AC: Why the Chart Runs Hotter

If one column of the TIG welding current chart confuses people, it is aluminum. The “one amp per thousandth” rule works beautifully on mild steel, then falls apart the moment you load 6061: the bead sits on the joint like a cold worm, the tungsten turns grey and lumpy, and the puddle refuses to wet out. More amps eventually produce fusion, so welders conclude aluminum is simply a hot metal. It is not. Aluminum is heat-hungry with a surface that fights you, and those two facts explain every ampere on the chart.

The Oxide Layer: 3,700°F Sitting on 1,220°F

Pure aluminum melts at roughly 1,220°F (660°C). The oxide skin that forms on it almost instantly melts at around 3,700°F (2,040°C), more than three times higher. That is like welding through a thin ceramic shell floating on the molten metal underneath, and wiping alone will not save the joint, because oxide reforms within seconds in ordinary air.

This is exactly why alternating current is normally preferred for manual GTA welding of aluminum and magnesium: the electrode-positive half strips oxide away with its cleaning action, while the electrode-negative half drives penetration into the base metal. Miller’s TIG welding setting calculator defaults to AC for aluminum for precisely this reason, since straight DCEN would clean nothing and bury the tungsten in heat. Prep still matters: mechanical cleaning and a dedicated aluminum cleaner for welding reduce how hard the arc has to work, and that shows up directly in the amperage you need.

Why the Chart Adds 10–25%

Start with the steel baseline of 1 amp per 0.001 in, then add the heat aluminum demands to break oxide, overcome its high thermal conductivity, and keep the puddle fluid. Most published guidance lands on 10–25% above the steel figure, and plenty of experienced welders simply run 1.2 amps per thou as a single-number shortcut. Weldclass’s TIG rules of thumb put common shop practice at roughly 1.5 amps per mm, the same idea wearing different units.

Thickness	Steel baseline (1 A/thou)	Aluminum starting point (×1.1–1.25)	Typical published range
0.063 in / 1.6 mm	~63 A	70–80 A	60–90 A
0.090 in / 2.3 mm	~90 A	100–115 A	90–130 A
0.125 in / 3.2 mm	~125 A	140–155 A	110–160 A
0.190 in / 4.8 mm	~190 A	210–240 A	180–250 A
0.250 in / 6.4 mm	~250 A	270–300 A	200–300 A

Starting points only. Real values shift with joint design, position, and travel speed.

Frequency and Balance: The Two Knobs Charts Never Show

Two AC settings change the effective heat at the joint even when the amperage readout never moves.

• AC frequency controls arc width. Mains-frequency machines run at 60 Hz (50 Hz outside North America) with a wide, soft arc, while inverter machines let you climb to 100–200 Hz, which narrows and focuses the arc for tighter control on thin and out-of-position work. A focused arc puts more of the same amperage into the joint instead of spreading it across neighboring metal.
• AC balance splits the cycle between cleaning and penetration. More electrode-negative time means deeper penetration and less cleaning; more electrode-positive time means a wider etched zone and shallower heat. Brands label this differently, with some dials reading “% cleaning” and others “% EN,” so check your machine’s manual before assuming direction.

The practical consequence: a heavily cleaning-biased balance wastes heat scraping oxide and puts less of it into fusion, so the same nominal 130 A welds cooler than a penetration-biased setting at 130 A. If your bead is wide, frosty, and shallow, fix balance before touching the amperage.

Thin Sheet and Cast Aluminum: Both Ends of the Scale

Thin sheet (0.063 in and under) is where raw chart values mislead most. The calculated amperage may be technically correct, but the metal saturates with heat in seconds, so chill blocks, a copper backup bar, a bigger gas cup, and a fast start are what actually keep the sheet alive. Heat sinking is the same priority in aluminum boat welding, where long runs on thin hull plate punish anyone who trusts the number alone.

Cast aluminum sits at the other extreme. Porosity, absorbed oil, and oxide inclusions mean the arc often has to burn through contamination before it reaches clean metal, so 1/4 in cast tooling plate or a cast engine case may need 150–180 A where solid 1/4 in 6061 would run comfortably on paper. Use a larger cup, keep travel steady, and consider gentle preheat on heavy castings, cautiously, since preheat adds total heat input to a part that may already be marginal metallurgically.

Two practical starting points:

1. 0.125 in 6061 lap joint, flat: start near 125 A (steel baseline), bump 15–20% to about 145–150 A, then dial with the pedal. Run ER4043 for general work or ER5356 where strength and corrosion matching matter, as covered in 5xxx-series marine alloy guidance.
2. 1/4 in cast aluminum engine case: set 160–180 A, bias balance slightly toward cleaning to break through casting contamination, use a larger cup, travel slowly and deliberately, and step down on the pedal as the casting itself heats up.

The same “run hotter but control it” mindset applies when aluminum moves to other processes; the aluminum MIG welding guide covers how spray transfer handles thick aluminum differently from AC TIG.

Beyond Amperage: Tungsten, Filler, Gas, and Arc Length

Two welders can set the same 120 amps on the same machine and get completely different beads. One gets a focused arc, a clean puddle, and a neat stack of dimes. The other fights a wandering arc, dips tungsten, and leaves porosity behind. The chart number was identical; the supporting variables were not. Amperage only works when the tungsten, filler, gas coverage, and arc length are matched to it.

Match Tungsten Diameter to the Current Range

Tungsten is the first place a good amp setting falls apart. A 2% ceriated or lanthanated electrode about 1/16 inch in diameter handles roughly 40 to 120 amps. Step up to 3/32 inch and the comfortable range runs about 80 to 200 amps. Those overlaps matter: a 3/32-inch electrode can run at 90 amps, but it will not focus as tightly as a 1/16-inch one at the same setting.

Go too large and the arc becomes lazy, wanders, or refuses to start; the current cannot keep the tip hot enough to emit electrons steadily. Go too small and the tungsten overheats, balls up, and sheds contamination into the puddle. If your chart says 70 amps, a 1/8-inch tungsten is the wrong tool no matter how carefully you set the dial.

Ground Point Versus Trivalent Point

A standard ground point is conical, with length roughly two to two and a half times the electrode diameter. Grind longitudinally, not around the circumference, and use a dedicated wheel so the tungsten does not pick up steel or aluminum residue. A trivalent, or three-leaf, point has three small flats meeting at the tip. It spreads the arc slightly, resists erosion better at high current, and suits production work where consistent arc shape matters. Neither point fixes an amperage mismatch, but a contaminated or blunt point will make a correct setting behave badly.

Filler Rod and Shielding Gas Complete the Circuit

Filler diameter follows the same logic. A common pairing guide uses 1/16-inch rod for roughly 60 to 120 amps and 3/32-inch rod for about 110 to 200 amps. Another practical rule is to match rod thickness to base-metal thickness. Too thin a rod at high current melts before it reaches the puddle; too thick a rod cools the puddle and forces you to slow down.

For gas, argon flow of roughly 15 to 25 CFH is typical for manual GTAW. More is not better. Excessive flow creates turbulence at the cup and can pull room air into the shielding envelope, causing porosity that looks like a gas shortage. Too little flow leaves the puddle exposed. A gas lens improves coverage and lets you use a larger cup, which helps on stainless and aluminum. Set pre-flow around one second and post-flow long enough to protect the cooling tungsten, usually three to eight seconds depending on amps. Contamination control starts before the arc; if you are welding aluminum, proper aluminum cleaner for welding prep matters as much as gas flow.

Arc Length Is a Heat Control You Can See

Aim for an arc length approximately equal to the tungsten diameter. That is the short, focused arc the chart assumes. Lengthen it and arc voltage rises at the same amperage, spreading heat over a wider area and producing a softer, shallower, wider bead. Shorten it too much and you risk touching the puddle, contaminating the tungsten, and losing visibility. Arc length is why two welders on identical settings get different penetration. The Weldclass TIG rules of thumb make the same point: keep the arc tight and let the pedal do the fine adjustment. The Miller TIG calculator is a useful baseline, but it cannot see your arc length.

Troubleshooting the Supporting Variables

Symptom	Likely cause	Amperage-related fix
Arc wanders or is hard to start	Tungsten too large for the current, or contaminated	Use a smaller diameter or raise amps into its rated range; regrind
Tungsten balls or blunts quickly	Tungsten too small, or amps too high	Step up one tungsten size or reduce peak current
Wide, shallow bead with weak penetration	Arc too long	Shorten the arc first; only add amps if penetration is still low
Porosity near the start	Pre-flow too short, or flow too high and turbulent	Set flow to 15–25 CFH and extend pre-flow; amps are usually not the cause
Narrow bead, cold toes, lack of fusion	Current too low for the travel speed or joint	Raise 5–10 amps and tighten the arc

The lesson is simple: treat amperage as one part of a system. Set the tungsten and filler to suit the current, cover the puddle properly, and keep the arc short. Then the number on the chart has a fair chance of producing the bead it promised. If you work in critical applications, the same discipline appears in aerospace TIG welding, where electrode condition and arc length are controlled as tightly as current.

Adjusting for Joint Design, Position, Travel Speed, and Fit-Up

Every chart value quietly assumes the same test piece: clean, well-fitted material, welded flat at moderate speed with nothing bolted to it. Real joints rarely offer all four. The chart sets a baseline; the joint in front of you decides which way to move.

Joint Geometry: Where the Heat Actually Goes

Amperage is fixed on the dial, but how much of that heat reaches the weld zone depends on geometry. Four common joints behave very differently at the same setting:

• Butt joints are the chart’s home turf: two edges, even mass on either side, so published values land close.
• Lap joints put the arc on an edge over a second sheet. The faying edge melts early while the sheet below acts as a mild heat sink, so amps stay near chart but travel speed usually has to slow.
• Inside corners (fillets) are the classic heat sink: two plates at 90 degrees pull heat away from the arc, so add roughly 10% over the flat-butt value, more on heavier fillets.
• Outside corners are the opposite: only thin edges to heat, and molten metal runs off them. Drop 10% or more below chart and keep the arc tight.

Same plate, same dial setting, four different outcomes: no single chart entry explains all of them.

Fit-Up, Root Gaps, and the Fixture Underneath

Poor fit-up is the quiet saboteur of thin-sheet TIG. A root gap leaves thin edges suspended in air with extra radiating surface area, and every clamp, tack, or table bolt attached to the part pulls heat straight out of the puddle. The working rule: add 5-15% current for sloppy fit-up and root gaps, and drop a few amps when the joint is tight, square, and well tacked.

Fixturing matters too. Weld a bracket to a heavy steel plate and it becomes a chill block drinking heat from the puddle; clamp thin sheet to a big steel table and you get the same effect. On material under about 0.050 in, a copper or aluminum backup block often lets you drop amps and still get full fusion. If you cannot move the part, plan to move the amps.

Position and Travel Speed

Gravity is free and it is always working against you. Out-of-position welding (vertical up, vertical down, overhead) typically calls for 10-15% less amperage than flat so the puddle stays viscous enough to stay where you put it. Published tools such as Miller’s TIG welding calculator bake this reduction in.

Travel speed is the other half of the equation, because amperage only controls heat input alongside time. Faster travel means less time over any point, so penetration drops and you need more amps to hold it. Slower travel soaks heat in, so back the pedal off. If your bead sits narrow and proud at normal speed, add current before you slow your hand.

Three Worked Scenarios

16-gauge (0.062 in) mild steel butt joint, 1/32 in gap, flat. Baseline is 62 amps, about one amp per thousandth. The gap adds heat sinking and extra edge surface, so start at 68-72 amps. If the root will not wet out, nudge up; if the tacks pull the gap closed, ease down.

3/16 in (0.187 in) mild steel fillet, vertical-up. Flat chart value is 185-190 amps. Removing 10-15% for position lands near 160 amps, though many welders settle at 140-155 amps, since the puddle tries to run ahead on the climb.

0.050 in stainless tube root pass. Baseline is 50 amps, but a tube root has no backing and the surrounding metal is a continuous heat sink that builds over a full circumference. Start at 40-45 amps and ease off as the tube warms; thin roots usually blow in the last quarter. Watch color: straw to light gold means control, grey or blue means the heat outran you. On code and aerospace TIG welding work, color limits are treated as requirements, not suggestions.

A Post-Pass Dial-In Checklist

Run through this after the first bead:

1. Bead profile: proud and convex means too cold or too fast; wide and flat means too hot.
2. Toe wetting: a ledge at either toe is lack of fusion; add amps or slow down.
3. Penetration: check the back face for a heat line, and on open roots for full fusion.
4. Heat buildup: later welds on the same assembly routinely need 5-10 amps less than the first.
5. Adjust in 5-10 amp steps and log the change with joint type and position.

The chart gets you to the ballpark. Geometry, fit-up, position, and travel speed decide where you actually stand.

Pulse TIG, Frequency, and Advanced Controls Where the Chart Stops Helping

Every chart so far assumes your machine delivers a steady, uninterrupted current once you strike the arc. That was reasonable in 1975. It is nearly useless on a modern inverter TIG machine, where one knob can split your amperage in half, chop it into pulses, shift its frequency, and taper it to nothing over the last half-second. This is where printed charts stop helping, and where welders learn the controls or wonder why identical settings weld differently.

Pulsing: Higher Peak Amps, Lower Average Heat

Pulsed GTAW alternates between peak amperage and background amperage. The machine holds peak for a set fraction of each cycle, then drops to a lower level for the rest. On most machines the background sits around 40–60% of peak current, and the time-at-peak share is the pulse duty or on-time.

Why bother? Heat input is not peak amperage. Pulse at 120 A peak with 40% duty and 50 A background and your average current lands far closer to 78 A than 120 A:

Average A = (peak × duty) + (background × (1 − duty))
= (120 × 0.4) + (50 × 0.6) = 48 + 30 = 78 A

That arithmetic is the whole trick: the wetting and penetration of a 120-amp arc, with heat soaking into the part like a 78-amp arc. On thin material, where the chart number either wets out or blows a hole, that gap decides a finished weld versus scrap.

Pulse frequency changes the character of the weld:

• 1–10 Hz (low frequency): Slow, visible pulsing. You watch the puddle freeze and re-melt. Great for thin sheet, gap control, and distortion on long seams, since the background phase lets the puddle cool first.
• 50–200+ Hz (high frequency): Too fast to see. The arc tightens, penetration narrows, and the heat-affected zone shrinks. Popular on stainless and anywhere cosmetic consistency matters.

Practically, pulsing lets you run above the chart value: if it says 90 A, a 110–120 A peak with a 40–50% background usually beats a flat 90 A, as long as travel speed matches the average, not the peak.

AC Frequency: The Control That Reshapes the Arc

On AC machines, frequency is a separate dial from balance. Raising it into the 120–200 Hz range narrows and concentrates the arc cone: deeper, tighter penetration and a smaller heat-affected zone. Lower frequencies, 20–60 Hz, give a wider, softer, cleaning-heavy arc for oxidized or cast aluminum.

Balance and frequency interact with your amperage: 150 A with a cleaning-biased balance can deliver less usable penetration heat than 150 A with penetration bias and higher frequency. The dial reads the same; the arc does not. On a stubborn or porous aluminum job, proper aluminum prep reduces the cleaning current you must burn through dirt before you change a setting. It is worth reviewing how proper aluminum prep handles that contamination at the source.

Downslope, Post-Flow, and Crater Control

Downslope is how long the machine ramps from welding current to zero after you release the pedal. Crater cracks form when current stops abruptly and the puddle freezes with a concave shrinkage crater, a defect especially common in aluminum. A downslope of roughly 0.5–2 seconds, matched to thickness and puddle size, fills that crater.

Post-flow keeps shielding gas over the cooling weld, protecting hot tungsten and the molten puddle from oxidation. Too little shows up as grey or sugared discoloration on stainless and titanium, and as contamination and porosity on aluminum. Pre-flow purges the torch line before the arc starts so an HF start does not contaminate the tungsten.

Why Inverter Machines Can Hold Numbers Transformers Cannot

Inverter GTAW machines hold stable arcs down to a few amps, around 5 A on DC, where older transformers turned erratic below 20–30 A. An inverter will hold a 30-amp arc on 22-gauge stainless while a transformer wanders or refuses to start, so low-amp chart rows for inverter capability are aspirational on transformer hardware.

When to Ignore the Chart and Set by Average Heat

1. Take the chart baseline for your thickness.
2. If pulsing, set peak 15–25% above that baseline.
3. Set background at 40–60% of peak and adjust duty until the average lands near the chart value.
4. Read the bead and correct in small steps.

Where the chart runs out is dissimilar thickness: 0.125 in plate to 16-gauge sheet. Set for the thicker side, use pulse and downslope to protect the thin side, and let travel speed and torch angle absorb the difference. A TIG welding calculator gives a solid baseline, but it cannot see your joint, fixture, or pulse settings. And if aluminum MIG welding suits the job better, that call comes first.

Common TIG Amperage Mistakes and How to Fix Them

Most ruined TIG welds come from welders who obeyed the chart too literally. The number you dial in is a hypothesis; the puddle is the experiment. The mistakes below share one root cause: the machine was set for thickness and never re-set for the actual joint.

Mistake 1: Setting by Thickness Alone and Never Adjusting

A chart gives a starting range, but it knows nothing about your joint. An inside corner traps heat and wants more amps; a thin outside corner edge melts away at the same setting. Poor fit-up turns the joint into a heat sink and needs more current than a tight butt joint of identical thickness. As a reference, Weldclass’s TIG rules of thumb recommend adding roughly 10 percent for poor fit-up or open root gaps, a small correction that fixes a large share of cold-lap complaints.

Mistake 2: Running Too Cold

A cold weld announces itself: a bead sitting proud and narrow, like dominoes laid on the plate instead of in it, with edges that never wet out. The arc never brought the joint to flow temperature, so filler piled up instead of fusing. On aluminum it is worse, a blobby, frosty bead with cold lap at the toes, because a cold arc also fails to break the oxide film. Good aluminum cleaning before welding removes that oxide, but chemistry cannot rescue a puddle twenty amps too cool. Add 5 to 10 amps, or slow down slightly.

Mistake 3: Running Too Hot

The opposite failure is louder but just as common: burn-through, a puddle that runs away, undercut at the toes, and a wide flat bead that is starved at the edges. On mild steel this is mostly cosmetic. On stainless it is a durability problem. Excessive heat causes sugar, heavy oxide on the back of an unshielded root, and drives the metal into the window where chromium carbides precipitate, robbing the heat-affected zone of corrosion resistance. When in doubt, back the current off and make up the difference with travel speed.

Mistake 4: Starting High and Never Easing Off

Many welders kick the pedal hard at arc start to get the puddle going, then never let up. On thin sheet that first second is where blowout happens. Downslope helps, but on a foot pedal the discipline is yours: start at full chart amperage only when the material supports it, and ease off as the puddle develops. If you cannot start cleanly at full amps, the setting is wrong for that thickness.

Mistake 5: Ignoring Heat Buildup on Successive Passes

A part gets hotter with every pass, so the fifth weld on a chassis needs noticeably less current than the first on the same nominal thickness. Fabricators welding thin sheet to a fixture often find they can drop 10 to 20 amps mid-job and still get identical penetration. Watch puddle behavior every few inches, not just at setup.

Mistake 6: Wrong Polarity

On an AC/DC machine it is easy to leave the switch on AC and weld steel all afternoon, or leave it on DCEN and try to weld aluminum. DCEN on aluminum gives almost no cleaning action, producing a black, sooty, unfused bead that looks like contamination but is a polarity problem. Steel, stainless, titanium, and copper alloys belong on DCEN; aluminum and magnesium belong on AC. If your machine’s setting calculator and your results disagree, check polarity first.

Tungsten Problems: Sticking, Ball Ends, and Contamination

Tungsten sticking to the puddle means the amperage is too low to sustain a stable arc, or the electrode touched the pool. Either way the electrode is contaminated and must be ground back to clean material before you restart. Do not just flick the ball off: alloy has transferred into the tungsten and the arc will wander. Shape matters too. A pointed or truncated end suits DC work; the balled end is largely a legacy of transformer machines on AC, though modern inverters with balanced waveforms favor a balled or truncated point on aluminum. And a correctly sized rod and tungsten makes the current you selected far easier to control out of position.

Symptom-to-Fix Quick Reference

Symptom	Likely cause	Correction
Tall bead sitting on surface	Current too low	Add 5–10 A or slow travel
Cold lap at toes (aluminum)	Too cold, oxide still present	Raise 5–15 A; clean joint
Burn-through in thin sheet	Current too high, travel slow	Drop 10–15 A; speed up
Wide flat bead, undercut toes	Excessive current	Reduce 10 A; shorten arc
Sugaring on stainless root	Too much heat, no purge	Reduce amps; add purge
Tungsten sticks to puddle	Too cold, or tip touched pool	Add amps; regrind tungsten
Grey, pitted, erratic tungsten	Contamination	Grind to clean material
Crater crack at arc stop	No downslope	Use downslope; ease pedal off

The pattern is the same in every row: read the bead, name the symptom, change one variable, usually amperage, and run it again. Charts get you to the starting line; your eyes finish the race.

Safety, Ventilation, and Standards Around the Arc

A current chart guides heat, not safety, and higher amperage increases risk. More heat means more visible smoke, more ultraviolet and infrared radiation, and more argon displacing breathable air. OSHA’s welding fact sheet states plainly that welding produces visible smoke containing harmful metal fume and gas by-products, and those by-products scale with arc energy, arc time, and base metal temperature. A 90-amp setting on clean mild steel is a different exposure than 180 amps on coated, oily, or painted stock.

Ventilation and Fume Exposure

Air movement comes first, respirators second. Where local exhaust hoods or booths are not used, OSHA 1910.252(c) specifies general ventilation of about 2,000 cubic feet per minute per welder as a minimum. Two TIG machines in a closed bay need twice the makeup air. Ceiling fans moving air around are not the same as exhausting it; in a small garage the options are an open door, a properly sized exhaust fan, or a fume-extraction torch.

Two exposures matter:

• Stainless steel. Welding stainless can generate hexavalent chromium. OSHA’s permissible exposure limit is 5 micrograms per cubic meter of air as an 8-hour time-weighted average, with exposure control programs expected when that level can be exceeded. NIOSH and industry guidance on hexavalent chromium emphasizes source capture at the arc, correct balance and travel speed to avoid excessive heat, and respiratory protection when engineering controls are not in place.
• Coated and contaminated metal. Zinc coatings, primers, cutting oils, and old galvanizing produce fumes unrelated to the base metal. Grind or strip the weld zone first; amperage controls heat, not what heat vaporizes.

Arc Radiation, Electrical, and Gas Hazards

TIG arcs are unshielded by flux, so the full spectrum hits eyes and skin. Welding shield lenses must filter intense ultraviolet and infrared radiation; GTAW typically uses a shade 8 to 12 filter depending on current. Screens or curtains protect others, because arc keratoconjunctivitis (flash burn) can be painless for hours. A full-length jacket, closed collar, and gauntlets protect against UV burns to forearms.

Electrical risk rises with capability. Modern inverter TIG machines hold stable arcs at low amps but can present high open-circuit voltage at the torch. Treat the stinger as live until the machine is off: check leads for scorched insulation, keep gloves and floor dry, connect ground before striking an arc, and never change tungsten with wet hands.

Gas safety is silent. Argon is heavier than air and collects in pits, tanks, and low corners. In confined spaces, inert gas creates an oxygen-deficient atmosphere without warning. Vent the far end of any purge, monitor with an oxygen meter, and never rely on feeling lightheaded as an indicator. Cylinder handling, regulators, and supply arrangements should be reviewed against a solid welding gas and supply safety guide.

Hot work controls apply: clear combustibles within a reasonable radius, cover or move what cannot be moved, keep a fire watch after stopping, and have an extinguisher within reach. Sparks from a 150-amp fillet travel farther than expected.

Standards, Codes, and When the Chart Stops Counting

For code work, the chart is irrelevant next to paperwork. AWS standards provide the framework: AWS D1.1 governs structural steel welding; AWS A5 filler classifications cover rods such as A5.18 for ER70S-2, A5.14 for ER308L, and A5.10 for 4043 and 5356 aluminum wires. A qualified Welding Procedure Specification sets amperage range, position, gas, and acceptance criteria, and it always governs over any published chart. Aerospace and pressure work add procedure qualification and traceable filler; see how aerospace TIG standards and training handle process control.

Hazard	Why it matters	Practical control
Metal fume and gas	Scales with current and arc time	2,000 cfm per welder or local exhaust at the arc
Hexavalent chromium (stainless)	PEL 5 µg/m³ over 8 hours	Source capture, lower heat input, respirator if needed
UV and IR radiation	Flash burn and skin burns	Shade 8–12 lens, screens, full coverage
Open-circuit voltage	Shock from live torch or wet conditions	Dry floor, inspected leads, ground first, power off for tungsten
Inert gas displacement	Argon pools in low, unventilated spaces	Ventilate, oxygen monitor, never work alone in a purge space
Fire	Sparks travel farther than expected	Clear combustibles, fire watch, extinguisher on hand

For a small shop, the program comes down to four habits: move the air, protect the eyes, check the floor and leads, and know which document governs the weld. None of it takes a big budget, and all of it matters more as amperage climbs.

Putting It All Together: A Five-Step Setting Workflow and Conclusion

Charts, rules of thumb, and troubleshooting tables only help when you turn them into a repeatable routine. The welders who stop guessing don’t have better memory — they follow the same sequence every time a new job hits the bench. Here is a five-step workflow that works whether you’re setting a machine from scratch or double-checking a saved program.

Step 1: Measure the Actual Thickness

Never trust the nominal gauge stamped on the paperwork. Sheared sheet edges taper, mill runs carry tolerance, and a “16-gauge” panel can genuinely measure thinner in the middle of an edge than the catalog suggests. Put digital calipers on the material in at least two spots and use the smaller number as your basis. On plate, check the corner you’re actually welding, not the mill test report. A few thousandths of an inch sounds trivial until you’re at 60 amps instead of the 75 the real thickness calls for.

Step 2: Calculate the Chart Baseline

Apply the arithmetic from the rules-of-thumb section: 1 amp per 0.001 inch for mild steel, roughly 10% less for stainless, and about 10–25% more for aluminum on AC. Adjust for thermal conductivity on exotics — copper and brass need substantially more, titanium and nickel alloys need less and tighter control. For a quick cross-check, the Miller TIG welding calculator walks the same logic with material, thickness, and joint inputs. Write the number down. You’re about to modify it, and having the baseline visible keeps your adjustments honest.

Step 3: Modify for Joint, Position, Fit-Up, and Travel Speed

Now apply the corrections: add 10–20% for root gaps and loose fit-up, add amps for inside corners and heat-sinking fixtures, subtract for outside corners and thin tapered edges, drop 10–15% out of position, and add if you plan to travel fast. If aluminum prep is part of the job, a proper clean matters as much as the number — see Aluminum Cleaner for Welding: How to Prep Aluminum Right before you blame the amperage for a dirty puddle.

Step 4: Match Tungsten, Filler, Gas, and Arc Length

The right amps with the wrong setup still fail. Size tungsten to the current range, pick filler rod roughly one diameter per 25–30 amps, set argon flow around 15–25 CFH with the right cup or gas lens, and hold an arc length about equal to the tungsten diameter. A long arc spreads heat and widens the bead without adding penetration, quietly undoing your calculation.

Step 5: Test, Read, and Adjust in Small Steps

Run a test bead on scrap of the same alloy, same thickness, and same joint configuration as the actual work. A flat coupon tells you nothing about a vertical fillet. Then read the bead: convex and sitting proud means too cold; washed out, undercut, or burned through means too hot. Nudge in 5–10 amp increments — TIG responds visibly to changes that small, and jumping 20 amps at a time skips right past the window.

Machine Presets Versus Manual Dialing

Modern inverters let you store chart-referenced presets for common jobs, which is a genuine time-saver in production. The risk is treating a preset as final. Presets assume ideal fit-up in the flat position; your part may be neither. Treat stored programs as Step 2 baselines and keep the dial or pedal under your hand for Steps 3 and 5. Manual dialing is slower on the first piece and faster on every piece after it, once your log gives you the answer.

Recap: Starting Values by Material

All figures below are starting points on material in the flat position with good fit-up:

Material	Thickness	Starting Amps
Mild steel	0.040 in (1 mm)	40–50 A
Mild steel	0.125 in (3 mm)	110–140 A
Stainless 304	0.062 in (1.5 mm)	45–60 A
Stainless 304	0.125 in (3 mm)	90–120 A
Aluminum 6061 (AC)	0.063 in (1.6 mm)	70–90 A
Aluminum 6061 (AC)	0.125 in (3 mm)	120–150 A
Aluminum cast (AC)	0.250 in (6 mm)	150–180 A
Copper	0.125 in (3 mm)	150–200 A

Run those through the workflow and they become yours, not the chart’s. A TIG welding current chart is training wheels: genuinely useful while you’re learning, gradually less consulted as the puddle teaches you what 5 amps up or down actually looks like. The chart gets you to the ballpark. The puddle — fluid, wetted out, flowing where you point it — is the final authority. Read that, log what you did, and within a few dozen joints you’ll find yourself reaching for the dial before you reach for the chart.

Frequently Asked Questions

What is the standard rule of thumb for TIG welding amperage?

For mild steel, the classic starting point is about 1 amp per 0.001 inch of material thickness — so 0.125 in (1/8 in) plate starts near 125 amps. In metric terms this is roughly 25 amps per 1 mm. Treat it as a baseline and adjust for joint, position, and fit-up.

How many amps do I need to TIG weld 1/8 inch aluminum?

Aluminum needs more current than steel of equal thickness because it conducts heat away so quickly, so many welders use 1.0-1.2 amps per thou. For 0.125 in aluminum, a practical starting range is roughly 110-150 amps on AC, with pedal control doing the fine work.

Why does stainless steel need less amperage than mild steel?

Stainless retains heat in the joint rather than conducting it away, so the puddle stays fluid longer at lower current. Most charts call for roughly 10-20% less amperage than mild steel of the same thickness, and out-of-position or heat-sensitive work may need even less to avoid heat tint.

Does a TIG current chart account for welding position and joint type?

No. Charts assume a flat butt joint with good fit-up. Inside corners and fixtures act as heat sinks and need more current, outside corners and edges need less, and vertical or overhead welding usually calls for 10-15% less amperage to keep the puddle from sagging.

How do tungsten diameter and arc length affect the current I should use?

Each tungsten size has a practical current window: 1/16 in works well around 40-120 A while 3/32 in suits roughly 80-200 A. Keep arc length about equal to the tungsten diameter, because a longer arc raises voltage and spreads heat wider even at the same amperage.

Should I adjust amperage between passes on the same part?

Yes. Each pass preheats the surrounding metal, so later welds often need less current than the first to reach the same puddle. Experienced TIG welders back the pedal off as a joint heats up rather than holding one fixed setting.

What role does pulsing play compared with a fixed chart value?

Pulsing alternates a peak amperage with a lower background level, cutting average heat input while still letting you penetrate at the peak. This lets you run a chart-level peak on thinner material with far less distortion, especially on thin stainless and aluminum.

Where does amperage fit into welding safety requirements?

Higher currents and longer arcs increase UV output and fume generation, so ventilation and eye protection matter. OSHA’s welding guidance addresses fume and gas control, and 1910.252(c) sets a minimum general ventilation rate of about 2,000 cfm per welder where local exhaust is not used.

Do code and procedure documents override a TIG current chart?

Yes. On qualified work, the written welding procedure specification defines the approved parameter range, and charts only help you stay within it. For AWS code work such as D1.1 structural welding, the qualified WPS always governs over any shop chart.