TIG Welding Cup Size Chart: Pick the Right Cup Every Time

A fabricator once spent an entire afternoon chasing pepper porosity across a stainless benchtop, turning the argon up, then down, then up again — only to find the real culprit was a #5 cup cranked to 25 CFH on a job that needed a #12. Shielding gas problems are usually cup size problems, and the right chart fixes them in minutes.

Why Cup Size Decides Your Weld Quality Before the Arc Even Starts

The fabricator had burned half a day chasing porosity on a stainless bench. Machine clean, tungsten sharp, still every bead peppered with pinholes. So he did what most of us do first: cranked the argon from 20 to 30 CFH. It got worse. He chased the regulator, the hose, and the electrode, then finally stared at the torch — and found a #5 cup, far too small for that joint, shoving far too much flow through a tiny opening. Too much argon through too small a cup doesn’t blanket the weld. It blasts it, creating turbulence that sucks room air into the puddle.

That afternoon compresses a lesson every TIG welder learns: shielding gas problems are usually cup size problems. Before you touch the amperage dial or blame the tungsten, look at the ceramic on the end of your torch. Get it wrong and it quietly sabotages everything downstream.

What a Cup Size Actually Means

Here’s the question most people search for, answered plainly: a TIG cup number is the inside diameter of the nozzle measured in sixteenths of an inch. A #6 cup has a 6/16-inch opening — 3/8 inch, about 9.5 mm. A #4 is 4/16 inch, 6.4 mm, and a #12 is 12/16 inch, 19 mm. The number isn’t a model code; it’s a direct measurement, which is why charts translate across brands.

What that number controls is the volume of gas coverage. A big cup holds a wide, deep column of argon around the arc; a small cup delivers a narrow, tight envelope. Neither is better on its own — the range runs from a micro torch cup around #3 for delicate work up to #24 and larger for heavy-coverage jobs.

Where the Cup Sits in the Torch Assembly

The cup isn’t an accessory bolted onto the side of the process. It’s the final gate shielding gas passes through, and its shape decides whether that gas exits as a quiet cone or a chaotic jet that pulls air in:

• Argon leaves the cylinder, then passes the regulator, hose, and solenoid.
• It flows down the torch body past the collet body or gas lens.
• It exits through the cup opening, shielding the tungsten and puddle.
• That shield displaces oxygen and nitrogen that would react with hot metal and ruin the weld.

Laminar vs. Turbulent Flow, Without the Physics Lecture

Shielding gas works best in laminar flow — a smooth, orderly column where the gas moves in one direction at one speed. Think of a calm faucet stream: clear, coherent, predictable.

When flow becomes turbulent, the stream fragments into eddies and swirls. A turbulent argon column doesn’t just fail to protect the puddle — it pulls atmospheric air into the shield, because swirling creates low-pressure pockets that draw more air in. Oxidation, porosity, and that pepper look follow. A gas lens or matched cup creates laminar flow; mismatched flow, cup size, and geometry create turbulence.

Miller Welds notes TIG shielding gas flow rates generally range between 10 and 35 CFH depending on consumables and ambient conditions. That window is wide because flow and cup size are a matched pair: what protects through a #12 cup can wreck a weld through a #5.

Three Things Cup Choice Quietly Controls

Beyond gas coverage, cup size shapes three practical aspects of every weld:

1. Visibility. Larger cups block more of your view, especially in tight joints. Clear Pyrex cups trade obstruction for line-of-sight.
2. Heat input comfort. The cup sets how close you can sit. Big cups allow longer arcs and hotter passes; small cups force you tighter and cooler.
3. Consumable life. A cup run above its rating, or thermally shocked, cracks and spalls. Right-sizing means fewer replacements.

This is where a chart-based method earns its keep. Instead of guessing, you read three inputs — material thickness, amperage, and joint type — get a starting cup number and flow rate, then tune by watching the puddle rather than turning knobs. The same discipline carries into aluminum MIG welding and every process where gas coverage decides the outcome.

Shielding gas discipline isn’t just about pretty welds. Weld fume and gas management fall under OSHA welding regulations (1910.252), and a stable, properly shielded arc means cleaner results and less rework, which is safer and cheaper. The cup is where good practice starts. Next, we’ll break down how those cup numbers are measured and matched to your torch.

How TIG Cups Are Numbered, Measured and Built

If the TIG cup numbering system seems suspiciously simple, that’s because it is. The number stamped on a nozzle is its inside diameter expressed in sixteenths of an inch. A #8 cup measures 8/16, which reduces to 1/2 inch. There is nothing more exotic to it, which is why welders can convert a cup size in their head mid-job instead of digging for a spec sheet. As TEC Products’ comprehensive cup guide explains, the whole sizing language traces back to plain fractions of an inch.

TIG Cup Conversion Chart

Cup number	Fraction	Inches	Millimeters
#4	4/16	1/4 in	6.4 mm
#5	5/16	0.313 in	7.9 mm
#6	6/16	3/8 in	9.5 mm
#8	8/16	1/2 in	12.7 mm
#10	10/16	5/8 in	15.9 mm
#12	12/16	3/4 in	19.0 mm
#16	16/16	1 in	25.4 mm
#24	24/16	1-1/2 in	38.1 mm

Three numbers to memorize because they cover most daily work: #8 = 1/2 inch (12.7 mm), #10 = 5/8 inch (15.9 mm), and #12 = 3/4 inch (19.0 mm). Standard alumina cups run from about #4 up to #12. Past that you’re into large specialty nozzles that reach #24 and beyond for extreme-coverage jobs like thick stainless or big-root purging.

Standard, Long and Extra-Long Nozzles

Length changes the gas just as much as diameter does. Argon leaving a short, stubby cup still carries the swirl picked up passing the collet body, so it breaks up quickly on contact with the surrounding air. A long or extra-long nozzle gives the gas room to settle before it exits, producing a smoother, straighter column that holds together over a wider area. The practical bonuses are better reach into tight joints and the ability to keep the torch body back out of your own line of sight. The tradeoff is bulk: a long #12 won’t fit where a stubby #8 will, and the added mass makes fine cup-walking motions clumsier.

Cup Materials and Styles

• Alumina (porcelain): The white opaque default. Cheap, heat-resistant, and available in every standard number. Brittle, though, and a dropped cup is usually a dead cup.
• Pyrex and quartz clear cups: Transparent glass-style nozzles such as CK Worldwide’s clear cup line. Same internal geometry as an equivalent numbered cup, but you can actually see the puddle and the tungsten tip through the wall.
• Long and “suffix” styles: Extended nozzles sold under suffixed part numbers for deep fillets, box sections, and root passes where the joint walls block a short cup.
• Back-purge and hood cups: Enclosed or side-outlet designs that feed shielding gas around the back of the weld zone, useful on stainless and titanium roots that would otherwise sugar.

Torch Compatibility, Threads and Gas Lens Fitment

Cups don’t attach to the torch; they thread onto the collet body, and that’s where compatibility gets people. Small air-cooled torches in the 9, 20 and 103/104 families use one thread size, while the classic 17/18/26 air-cooled group and their water-cooled 20-series equivalents use another. A cup that screws onto your buddy’s WP-18 may not touch your WP-9. Before buying, confirm three things: the thread on your existing collet body, whether it’s a plain or gas lens design, and whether your torch can handle the heat a larger cup invites. Hobbyist Welding Academy’s cup selection guide covers the matching rules in detail.

The trap is mixing ecosystems. Gas lens collet bodies have their own cup threads and sealing surfaces, so a standard cup generally won’t seat correctly on a gas lens body, and vice versa. Buy the collet body and cup as a matched pair. On high-amperage water-cooled work this matters less for the torch itself, but a big ceramic cup still radiates heat back at your hand and at nearby lines.

For thin, precise work where heat and puddle control are critical — aerospace, instrument tubing, small chamfers — a correctly sized cup on a compact torch matters more than raw gas volume. Our Aerospace TIG Welding: Standards, Techniques, and Training guide walks through how tightly those setups are specified. And regardless of cup style, keep the gas path clean: soot, machining oil, or a cracked cup interior will ruin shielding long before the flow rate does, as Miller’s shielding gas best practices reiterate.

The Complete TIG Welding Cup Size Chart

This is the table most welders end up taping inside a cabinet door. Read across: pick the row that matches your material thickness, confirm the amperage range fits your setting, then set argon flow to the CFH listed for that cup. Every figure below is a starting point for a standard (plain collet body) setup in still air, not a legal requirement.

Standard Cup Size Chart (Plain Collet Body)

Cup #	Inside Diameter	Material Thickness	Welding Current	Argon Flow (CFH)
#4	1/4 in (6.4 mm)	Up to 1/16 in (1.6 mm)	0–50 A	5–10
#6	3/8 in (9.5 mm)	2–4 mm	100–150 A	12–15
#8	1/2 in (12.7 mm)	4–6 mm	200–250 A	18–22
#10	5/8 in (15.9 mm)	5–8 mm	250–350 A	20–25
#12	3/4 in (19 mm)	8 mm and heavier	350 A and up	25–30

A #5 cup sits between the first two rows and is a handy bridge for thin tubing around 1.6–3 mm where a #4 starves the puddle and a #6 floods the joint. Notice the pattern: as the cup number climbs, the coverage area grows faster than the number does, because area scales with the square of the diameter. That is exactly why the popular “double the cup number” shortcut under- or over-shoots on larger cups, a point we will unpack in the flow section.

A widely used heuristic backs the table up: run roughly 2–3 CFH of argon per cup size number. A #10 cup wants about 20–30 CFH, a #6 about 12–18. The Weldmonger quick reference pairs a #10 ceramic cup at 20–30 CFH with carbon steel on DCEN, and a Furick #12 at 24–36 CFH with stainless on DCEN. Stainless sits at the top of each range because it needs a wider, heavier blanket of gas to keep oxygen out of the hot zone.

Gas Lens Flow and Tungsten Stick-Out

Setup	Typical Flow (CFH)	Tungsten Stick-Out
#6 plain collet body	12–15	1–1.5 × electrode diameter
#8 plain collet body	18–22	1–1.5 × electrode diameter
#8 gas lens	10–15	Up to about 1/2 in (12 mm)
#12 gas lens	18–25	Up to about 1/2 in (12 mm)

Because a gas lens straightens the stream into a coherent column, you get equal or better coverage at noticeably lower flow and can stretch the electrode out for visibility. CK Worldwide’s gas lens documentation and HPA’s cup selection guide both describe this same relationship: less turbulence, longer stick-out, lower flow.

How to Adjust the Chart in Real Joints

The numbers assume a flat butt joint, torch perpendicular, cup about 1/4 in from the work, and calm air. Change any of those and you change the answer:

• Joint type: An inside corner traps heat and reflects gas, so you can go one cup size smaller than the chart and still get full coverage. A lap or open root often wants the next size up.
• Position: Out-of-position and vertical-up work means gas rises away from the puddle. Shrink the cup slightly, close the distance, and lean on a gas lens for a steadier column. Precision positional work is a big part of aerospace TIG welding practice.
• Torch angle: Any push angle beyond about 15° pushes the gas envelope ahead of the puddle. Re-center the cup or accept that you need more flow.
• Cup-to-work distance: Double the distance and you roughly double the flow needed to hold the same coverage. Keep the cup close.
• Ambient drafts: Per Miller’s shielding gas best practices, even a light breeze can strip shielding from the puddle. Fix the airflow before you crank the regulator; beyond about 30–35 CFH on a normal cup, extra gas turns turbulent and starts pulling air in rather than keeping it out.

Treat the chart as a calibrated guess. Set the listed flow, run an inch of bead, look at the result, then tune up or down by 2–3 CFH while watching the puddle. The arc, not the table, has the final word.

Standard Collet Body vs Gas Lens: What Changes on the Chart

Two welders can run the same #8 cup at the same 15 CFH and get completely different shielding. The difference is usually the part hiding behind the cup: the collet body. Swap a plain collet body for a gas lens and the numbers on the chart shift with it, so it is worth understanding exactly what changes before you start turning the flow meter.

What a Plain Collet Body Does

A standard collet body is a simple fitting. Argon enters through the back, passes around the collet, and exits through one or two small side ports plus a central opening. Because the gas is squeezed through narrow openings at speed, it leaves as a fast, swirling jet that mixes with air almost immediately, leaving the edge of the shielding envelope ragged. At low flow the coverage is thin; crank it up and the turbulence gets worse, because the swirling jet entrains surrounding air rather than pushing it away. As Miller’s shielding gas guidance puts it, more flow is not automatically better flow.

What a Gas Lens Does Differently

A gas lens replaces those ports with a stack of fine stainless steel screens. Gas passing through several layers of mesh is broken into hundreds of tiny parallel streams and straightened in direction of travel. The result is a wider, calmer, more uniform column of argon that stays coherent farther from the cup. In plain language: a collet body sprays gas like a hose with a broken nozzle, while a gas lens pushes it through a diffuser.

That smoother flow buys three practical things:

• Longer tungsten stick-out. Because the gas column holds together past the cup lip, you can extend the tungsten farther for better visibility in fillets and lap joints without starving the arc.
• Lower flow for equal coverage. The same shielding quality usually arrives at a reduced CFH setting, since less gas is wasted to turbulence.
• Better tolerance of drafts. A calmer, denser envelope resists mild shop air movement better than a swirling jet.

Factor	Standard Collet Body	Gas Lens
Flow pattern	Swirling, turbulent jet	Straightened, laminar column
Typical flow for a #8 cup	Roughly 15–20 CFH	Roughly 10–15 CFH
Tungsten stick-out	Collet body depth	Noticeably longer
Best fit	Small cups, AC aluminum, tight joints	Steel, stainless, open joints, #8 and up

Those ranges line up with the TIG settings chart and TEC Products’ cup guide.

Where Gas Lenses Stop Helping

Here is the part the brochures skip: below about a #6 cup, a gas lens does very little. The screens still straighten the flow, but the opening is so small that the gas column re-expands and turns turbulent within millimetres of the lip. Experienced welders on the Welding Tips and Tricks forum have long argued that a gas lens under #6 is effectively pointless for turbulence reduction. Keep your #4 and #5 cups on plain collet bodies and spend the money on bigger sizes instead.

The practical sweet spot is the #8 gas lens, routinely described as the universal setup. It handles everything from light sheet to medium plate on steel and stainless, gives good visibility, and fits most standard torches. Larger lenses such as the #12 suit heavy steel and stainless beads where a wide, slow-cooling blanket of gas protects the hot metal longer.

The AC Aluminum Exception

Aluminum on AC is where the gas lens advantage often reverses. The arc wanders more, the cleaning action extends beyond the visible bead, and a wide laminar column can make the etched zone harder to judge. Many experienced aluminum welders get better results with a plain collet body and a smaller cup, sometimes as small as a #5 or #6, because the tighter envelope matches the shorter arc length and keeps the cleaning band readable. A #12 gas lens that glories on mild steel is not recommended for AC aluminum work. If aluminum is your main focus, start with proper surface prep — our aluminum cleaner for welding guide covers the degreasing and brushing steps that shielding gas cannot fix.

The takeaway for reading the chart: pick your cup number from the thickness and amperage columns first, then decide whether you are running a standard or gas lens, and read the corresponding flow column. Never apply gas lens flow rates to a plain collet body, or assume a lens will rescue a cup that is simply too small for the job.

Choosing Cup Size by Metal: Steel, Stainless, Aluminum and Exotics

The chart gives you a starting number, but the metal in the fixture gets the final vote. The same 120-amp lap joint can be perfectly happy with a #6 on mild steel and demand a #12 plus a long post-flow in stainless. The difference isn’t amperage, it’s chemistry: how fast the alloy oxidizes, how far that oxidation spreads, and how long the metal stays hot enough to keep reacting after the arc moves on. Amps and thickness come from the settings side of the equation, and a good baseline is the Weldmonger TIG settings chart. The material decides the cup.

Carbon and Mild Steel: Small Cup, Modest Flow

Mild steel sits at the forgiving end of the spectrum. Its oxide film is thin, it doesn’t keep growing at red heat the way stainless oxides do, and the puddle tells you within seconds if something is off. Most mild steel TIG work lives somewhere between a #4 and a #8, with flow in the mid-to-high teens CFH through a standard collet body.

The usual failure on carbon steel is too much flow, not too little. Crank the regulator up and the gas column exits the cup fast enough to go turbulent, pulling surrounding air into the shield; the result is fine dark porosity scattered across the bead, the classic “pepper.” Back the flow down, or move to a gas lens that calms the stream, and it clears up. Too little flow looks different: a sluggish puddle with brown specks melting in and a film of oxide. Miller’s shielding guidance puts it plainly — more flow stops helping the moment the column turns turbulent. Best practices for proper shielding gas in TIG welding

Stainless Steel and Nickel Alloys: Bigger Cups, Longer Post-Flow

Stainless is where cup size starts costing real gas money, and where skipping it costs far more in rework. Chromium needs oxygen to rebuild its passive layer, but at welding temperature that reaction produces heavy oxide: heat tint on the visible face and, on the back side of an unguarded root, the rough blue-black scale welders call sugaring. Nickel alloys behave similarly, with sluggish wetting that rewards a wider, calmer gas envelope.

So stainless TIG commonly runs #10 to #12 cups at higher flow than you would use on steel, with a post-flow long enough to keep the puddle covered until it stops glowing — many procedures specify 10 to 20 seconds. Root passes on pipe or tube need a back purge as well; shielding the top does nothing for the underside. When tint shows up anyway, the fix is usually coverage width and duration, not lower amps. TIG cups: a comprehensive guide

Aluminum on AC: Keep the Cup Small and the Arc Stable

Aluminum is the exception that catches people out. AC welding needs a concentrated cleaning zone right at the joint, and the arc is already busy switching polarity sixty times a second. Hang a big cup or a gas lens on the torch and many setups answer with a soft, hissing, wandering arc that drifts more than the puddle does. That is why AC aluminum work typically stays around #5 to #8, on a standard collet body, with a short, firm stick-out. HPA: choosing a gas cup or gas lens

Upstream prep matters even more here than cup choice. Aluminum’s oxide film has to come off before the arc strikes, and a dedicated aluminum cleaner and proper prep routine will improve weld appearance more than any cup upgrade.

Titanium, Inconel and Other Reactive Alloys

Titanium, zirconium and most nickel superalloys keep reacting with oxygen and nitrogen well after the arc has passed. A titanium bead that looked fine at temperature can cool chalky white or violet if shielding stopped at the puddle’s trailing edge. These alloys want the largest practical coverage: a #12 or bigger, heavy post-flow, purge dams or trailing shields that carry protection behind the torch, and a draft-free work area. Aerospace shops treat shielding as a documented process parameter rather than a guess — see aerospace TIG welding standards and training for how tightly that is controlled. Corrosion-resistant alloys in the same family, such as Alloy 20, reward the same wide coverage and patient post-flow.

Cup Choice by Metal at a Glance

Material	Typical cups	Flow approach	Extra shielding
Carbon / mild steel	#4–#8	Modest; watch for turbulence	Rarely needed
Stainless steel	#10–#12	Higher flow, long post-flow	Back purge on roots
Aluminum (AC)	#5–#8	Moderate; standard collet body	Clean, dry joint first
Nickel alloys	#8–#12	Higher flow, patient post-flow	Wider envelope aids wetting
Titanium / reactive	#12+	Heavy post-flow	Trailing shield plus purge

Watch the weld as it cools, not just the arc while you are welding. That color is the fastest feedback loop you will get on whether your cup matched the material — and it is the habit that makes every cup chart work better.

Argon Flow, Cup Size and Torch Technique Working Together

Picking a cup off the chart only delivers argon to the mouth of the nozzle. What happens next depends on gas speed, cup-to-puddle distance, torch angle, and the air around you. Two welders with identical #8 cups can get very different results, and flow setting is usually the difference.

Why “Cup Number Times Two” Gets the Math Wrong

The oldest TIG rule of thumb says set argon to twice the cup number: a #8 gets 16 CFH, a #12 gets 24. It works mid-range and fails at both ends, because a cup number is a diameter in sixteenths of an inch while gas must fill a column’s cross-sectional area, and area scales with the square of that diameter. Double the diameter and you have four times the opening to cover, not twice.

Cup	Inside diameter	Opening vs a #5
#5	5/16 in (7.9 mm)	1.0×
#8	1/2 in (12.7 mm)	2.6×
#10	5/8 in (15.9 mm)	4.0×
#12	3/4 in (19.1 mm)	5.8×

So a #10 cup does not need double a #5’s flow. It needs closer to four times the volume to hold the same exit velocity at the cup mouth, which is what keeps oxygen out of the arc. Run times-two on a #12 at 24 CFH and the first draft walks straight into the puddle. CK Worldwide’s guidance on gas saver setups puts most applications at 15 to 20 CFH, starting low and increasing only as the joint demands, matching Miller’s shielding gas best practices.

Pre-Flow and Post-Flow: The Seconds Nobody Sets

Pre-flow of half a second to one second purges the air sitting inside the cup before you strike up, which matters most on stainless and titanium. Post-flow protects the solidifying bead and heat-affected zone after the pedal lifts: about one second per ten amps, capped at ten to fifteen seconds. Cut it to two seconds on a stainless root pass and heat tint creeps backward along the bead.

Torch Angle, Cup-to-Work Distance and Position

Coverage shrinks the moment you tilt the torch. At a 10 to 20 degree travel angle the envelope leans with it, leaving the trailing edge less protected than the leading edge; past about 25 degrees you blow argon ahead of the arc and away from the joint. Cup-to-work distance matters as much: a cup dragged on the surface gives tight coverage, while floating it a half inch off dilutes the envelope before it arrives. Overhead sheds hot gas upward off the work, while vertical-up convects heat above the cup. In aerospace TIG welding, cup distance is treated as a fixed variable.

Drafts, Ventilation and the Air You Cannot See

Argon is about 38 percent heavier than air, so it pours off a horizontal surface and slumps out of vertical joints. Shop airflow is the silent variable: a fan or an open bay door can strip a shield that held perfectly ten minutes earlier. Deliberate ventilation follows rules of its own, and OSHA 1910.252 requires mechanical ventilation in confined or poorly ventilated areas, with general dilution ventilation of at least 2,000 CFM per welder unless local exhaust is used. Inside a booth or tank that same airflow can destroy your shielding, so local exhaust must sit away from the arc. A larger cylinder and a properly set regulator from a supplier like Airgas welding supplies keep flow steady.

Too Little vs Too Much: Reading the Symptoms

Symptom	Likely cause	Fix
Dull gray, crusty bead	Too little gas, or a draft	Add 2 to 3 CFH, drop the cup, kill the fan
Pepper porosity over the bead	Turbulence, usually too much flow	Reduce flow, or step up cup size
Arc hisses, sizzles or wanders	Excess exit velocity at the cup mouth	Back flow off until the arc is quiet
Sugaring or heavy tint on stainless	Coverage too narrow, post-flow too short	Bigger cup, longer post-flow, back purge

The Five-Minute Tuning Procedure

1. Set flow at the low end of your cup’s chart value, say 12 CFH for a #8.
2. Run a test bead on scrap of the same alloy, thickness and position as the real joint.
3. Watch the puddle: clean, mirror-bright metal means coverage is adequate.
4. Add argon in 2 CFH steps until the surface clears, and note that number as your baseline.
5. If the arc turns noisy or wanders, you have gone past the top. Back off a couple of CFH.

Flow tuning cannot fix a dull, cloudy aluminum bead that never clears. When shielding is correct, base-metal cleanliness is usually the culprit, and proper aluminum cleaning before welding solves more of those problems than any cup size. The chart sets the baseline; the puddle delivers the verdict.

Specialty Cups and When the Chart Doesn’t Apply

The cup size chart assumes an easy life: a flat plate, an open joint, a steady hand, and clear air around the puddle. Real work rarely cooperates. A root pass buried in a fillet, a header tucked against a frame rail, a roll joint on pipe at 2 o’clock — in these spots, geometry overrides amperage, and the “correct” cup from the chart becomes the wrong cup in practice. Knowing which specialty nozzles exist, and when to abandon the chart’s baseline, separates a clean tie-in from a night of grinding out sugared roots.

Long and “Suffix” Nozzles: Letting the Gas Settle

A longer nozzle gives shielding gas more distance to straighten before it leaves the cup. Gas exiting a short #5 cup is still expanding and curling at the edges; through a long or extra-long nozzle of the same inside diameter, the flow has room to develop into a smoother, more laminar column that reaches deeper into a joint. That is why manufacturers list “long” and “extra-long” variants of popular sizes — same coverage diameter, better reach. Deep butt joints, closed root passes, and anything with a narrow V-groove benefit most, because the stream can penetrate the groove instead of washing across the top of it.

Back-Purge and Hood Cups

Stainless, duplex, and nickel alloy roots oxidize on the underside as readily as they discolor on top. Back-purge or “hood” style cups attach at the rear of the torch body and split the gas supply: part of the argon shields the arc, part is ducted to the back of the joint for purging. For critical stainless tubing, this is far more reliable than taping a hose to one end of the pipe. Pair a hood cup with a slightly longer post-flow and you protect both faces of the weld with one setup. Tec Products’ cup guide walks through the common purge configurations and their flow ranges.

Periscope, Angled and Out-of-Position Cups

When the torch body physically cannot sit square to the weld, angled or periscope nozzles bend the gas path around the obstruction while keeping the tungsten pointed where it needs to be. They are a favorite on exhaust manifolds, inside-corner brackets, and stacked structural work where the handle would otherwise drag on the fixture. Out-of-position welding adds a second complication: gas rises, so overhead and vertical-up passes need tighter, faster coverage rather than a big lazy envelope. This is where technique and consumables meet, and where a good all position welding rod choice helps you keep travel speed up so gravity never gets time to flatten the puddle.

Micro and Spot-Welding Cups

At the other end of the scale, micro torches start around a #3 cup for instrument, jewelry, and thin-gauge work running well under 50 amps. Coverage there is a small, precise envelope — anything larger just wastes argon and blurs your view of a puddle the width of a pencil lead.

Cup Walking With Big Clear Pyrex

Large clear cups have made cup walking popular again on pipe and long structural passes. The cup rests on the joint and rolls in a smooth figure-eight while the arc stays buried underneath, and the transparent wall lets you watch the puddle the whole way. A #16 or larger Pyrex nozzle maintains coverage even as the cup slides, provided your flow is steady and your tungsten stick-out is consistent. Watch for one quirk: glass retains heat differently than alumina, so repeated heavy passes can get the nozzle hot enough to matter — let it cool rather than wiping it.

When Joint Geometry Forces a Smaller Cup

An inside corner traps heat and physically blocks a wide nozzle from getting close to the root. Even at 150 amps, a #10 may simply not fit — so you drop to a #6 or #8, keep the cup tight to the work, and accept the narrower coverage because there is no alternative. Lap joints, root passes, and tacks against fixtures behave the same way. If a big cup will not reach, a smaller cup with a gas lens often restores the coverage you lost.

Improvising Coverage: Gas Lens Plus Trailing Shields

Where no off-the-shelf cup fits, combine a gas lens with a trailing shield or a homemade argon sock behind the weld. The lens straightens flow at the arc, the shield extends protection over the cooling bead — exactly what titanium and aerospace TIG welding specs demand when the metal stays reactive until it is below roughly 800°F. Extending post-flow is the cheap version of the same idea: Miller’s shielding gas best practices note that cooling metal keeps absorbing oxygen, so coverage has to outlast the glow.

The lesson is simple: treat the chart as your baseline for open, flat, draft-free joints, then let access, joint geometry, and material rewrite the rules. Keep one or two specialty nozzles in the cart and you will rarely be stuck improvising mid-job.

Common Cup Size Mistakes and How to Troubleshoot Them

Most cup problems never announce themselves as cup problems. They show up as a dirty puddle, a tinted weld, a cracked nozzle, or a wandering arc, and the reflex is to reach for the flowmeter instead of checking what is screwed onto the torch. Work through the symptoms below in order.

Pepper Porosity: Too Much Gas, Not Too Little

Pepper porosity is the classic misread. When a weld comes out speckled with tiny pinholes, most welders turn the argon up. On a plain collet body that usually makes it worse: excessive flow goes turbulent, the gas rolls back on itself and pulls surrounding air into the shield, the arc gets noisier, the puddle turns lazy, and oxygen ends up in the metal. Just as often the cup may be too small for the weld zone, so the trailing edge of the puddle sits outside the argon envelope and picks up air as you travel. Miller’s shielding gas best practices make the same point: more flow is not automatically better coverage.

Sugaring and Heat Tint on Stainless

Straw, purple, or blue discoloration on stainless means coverage ran out of time, not volume. The front may be perfectly shielded while the trailing zone, still red hot, drops below the argon blanket. Heavy black “sugaring” on the back of an autogenous root is the same failure with the stakes raised. The usual fix is a bigger cup plus longer post-flow, and on root passes an actual back purge. If joint geometry will not accept a bigger cup, slow down or shorten the weld segment so the hot zone stays under gas longer.

Cloudy Gray Aluminum

A dull, chalky, gray AC bead is usually contamination rather than shielding alone. Oxide and oil left on the plate cloud the cleaning zone and rob the arc of stability. Prep is half the fix: brush with a dedicated stainless brush and the right solvent, as covered in Aluminum Cleaner for Welding: How to Prep Aluminum Right. The other half is a smaller cup that keeps the cleaning band predictable instead of washing the whole area with an oversized envelope.

Symptom, Cause, Fix

Symptom	Likely cause	Fix
Pepper porosity, noisy arc	Excess flow on a plain collet body	Drop 3–5 CFH; check cup-to-work distance
Porosity only at the weld tail	Cup too small for travel speed and weld width	Step up one or two cup sizes, or slow the travel
Straw/purple tint on stainless	Post-flow too short or cup coverage too narrow	Bigger cup; extend post-flow 2–4 seconds
Black sugaring on root pass	No back purge, hot side exposed to air	Purge the back side; consider a hood-style cup
Cloudy gray aluminum bead	Surface contamination or weak cleaning zone	Clean properly, tighten cup, verify AC balance
Arc wanders off the tungsten	Stick-out too long for the cup	Keep stick-out within roughly the cup’s inside diameter
Cracked or chipped nozzle	Thermal shock, hot pliers, or a drop	Replace it; keep spares on the cart
Gas lens gives no benefit	Lens in a cup below about #6, or flow set for a plain body	Match flow to the collet body installed

Ceramic Cups Crack: Cheap Part, Expensive Downtime

Alumina cups are brittle. Set a hot nozzle on a steel bench, grip it with pliers while it glows, or drop it from cart height, and it chips or splits. Gas then exits through the crack, the pattern breaks down, and you are back to porosity. Treat nozzles as disposable: keep a couple of each size, let them air-cool, and never torque them with a wrench. CK Worldwide’s consumable guidance puts it plainly: ceramic nozzles are inexpensive wear items, not tools to be nursed along.

Two Setup Errors That Quietly Ruin Good Settings

The first is flow mismatch. Gas lens flow rates differ from plain collet body rates, and swapping one without resetting the flowmeter leaves you over- or under-gassed while the chart says everything looks fine. The second is the forgotten stick-out: lengthen the tungsten after a cup change and you have moved the arc root outside the designed envelope, changing coverage and arc focus in one motion. Re-check both whenever anything on the front of the torch changes. HP Academy’s cup and gas lens breakdown reinforces that cup, collet body, stick-out, and flow are one system, not four separate dials.

Keep the diagnosis order simple: confirm the consumables are correct, then the flow, then the technique. Nine times out of ten the arc will tell you which one was wrong.

Setting Up Your Cup Kit: Buying, Fitting and Shop Practice

Think of your cup kit like a socket set. You do not need every size on the wall, but you do need the handful that covers most of the work landing on your bench. Welders who buy cups one at a time, usually as replacements, end up with a drawer full of duplicates and no #8 gas lens when they need one. A little planning costs less than an afternoon chasing porosity.

The Starter Kit Worth Owning

Five pieces handle most steel, stainless and aluminum jobs in a general fabrication shop:

• #5 standard cup: tight spaces, small fillets, thin material and low-amperage detail work.
• #6 standard cup: the everyday default for light steel and positional work where a larger cup will not fit.
• #8 standard cup: mid-range brackets, thicker sheet and a comfortable starting point for beginners learning puddle control.
• #8 gas lens setup: collet body plus cup, and the versatile all-rounder for stainless and clean steel.
• #12 gas lens setup: wide, calm coverage for long stainless runs, heavy sections and work where discoloration matters.

Add sizes as jobs demand them: a #10 or #16 for heavy plate, a #4 or torch-specific micro cup for instrument work, and clear Pyrex cups if you want a better view of the puddle and the joint ahead.

Check Fitment Before You Spend a Dollar

The most common buying mistake is assuming cups are universal. They are not. Consumables must match both your torch series and your collet body threads, and a gas lens collet body is not interchangeable with a plain one. Gas lens bodies are longer, use different internal screen stacks and seat differently in the torch head. A cup that threads onto a WP-9 style head may not fit a WP-20, a water-cooled 100/200-series torch or a smaller micro torch, and the reverse is equally true.

Before ordering, confirm your torch model and cooling type, the thread or backend standard it uses, and whether the cup is made for a plain collet body or a gas lens. Reputable suppliers publish fitment charts, and cross-checking against the CK Worldwide consumables reference can save a return shipping label.

Brand ecosystems matter too. CK Worldwide, Furick-style cups and the WP-numbered torch family each have their own threads and accessories. Mixing brands can work with the right adapter, but it adds a variable that is easy to forget when someone else picks up your torch. If you shop gas and consumables together, this Airgas welding supplies guide covers what a typical TIG setup needs beyond the cup itself.

Care, Cleaning and Labeling

Ceramic and alumina cups are tougher than they look, but they fail in predictable ways. Soot and silicone deposits build up inside the nozzle and disrupt gas flow long before you notice them visually. Clean cups regularly with a dedicated soft brush or an appropriate solvent soak, and retire any cup that looks glazed or chalky.

Cracks usually come from thermal shock combined with mechanical stress: pliers gripped onto a hot nozzle, a torch dropped on concrete, or a cup snapped on while the metal is still warm. Let parts cool, hand-thread them, and keep spare #6 and #8 cups on the cart.

Labeling sounds fussy until two welders share a machine. Mark cups with size and type, such as “8 GL” for a #8 gas lens, using permanent marker or colored tape bands. Store plain and gas lens cups in separate compartments, because two cups that look identical from the outside can have completely different internals.

Shop Standardization and the Gas Bill

Consistency is the quiet payoff of an organized kit. When every station runs the same #8 gas lens on stainless and the same #6 standard cup on thin steel, relief welders reproduce results instead of re-diagnosing them, and new hires learn one system rather than five habits. Taping a card to the machine with the chosen cup, stick-out and flow rate turns tribal knowledge into something a precision-oriented welding program would recognize as procedure. Training resources such as an aluminium welding course reinforce the same discipline: measure, record, repeat.

Right-sizing flow also saves gas. Oversized flow on a small cup is pure waste, and manufacturers market gas saver kits with claims of up to about 40% argon savings when flow, cup and lens are matched properly. Treat that as a marketing figure rather than a guarantee, but the direction is sound: smaller, calmer, correctly sized coverage costs less per foot of weld.

Quick Reference Recap and Conclusion

Nine sections later, the whole method fits on an index card. Cup selection is not a guessing game and it is not a flowmeter numbers game either. It is a short, repeatable sequence that starts with the metal in front of you and ends with your eyes on the puddle. If you remember nothing else from this TIG welding cup size chart, remember the order of operations, because that order is what keeps you from turning the gas up when the real problem was a cup three sizes too small.

The Five-Step Decision Flow

1. Read thickness and amperage first. Before a cup touches the torch, know the material thickness and the current range it puts you in. Those two numbers narrow the chart down to two or three realistic cup numbers.
2. Pick the cup number. Take the inside diameter in sixteenths, check it against the chart, and land on a starting size rather than a favorite size.
3. Choose standard collet body or gas lens. Access, joint geometry, and material drive this more than preference does. A gas lens earns its keep on stainless and thick steel where you want a wide, calm envelope; a plain collet body still behaves better on AC aluminum work, where the cleaning zone wants a tighter, more focused shield.
4. Set flow in the right band. As a practical starting point, small cups in the #4 to #6 range run about 5 to 15 CFH, a #8 sits around 18 to 22 CFH, and #10 to #12 cups live in the 20 to 30 CFH range. Gas lens setups generally want a little less flow than people expect, because the straightened column covers more area per CFH.
5. Tune by the puddle, not by the dial. Add gas until the oxide cleans up and the arc runs quiet, then stop. If the arc hisses, wanders, or picks up an erratic sound, you have pushed past the useful point and are drawing air in through turbulence.

Let the Weld Be the Final Authority

Here is the part most welders learn the hard way: the flowmeter reading is a suggestion, and the weld is the verdict. The chart gives you a defensible starting point, but the arc, the puddle, and the finished bead are what confirm or overrule it. A mirror-bright stainless root that never sugared is proof the setup worked. A dull gray bead or a scatter of pepper porosity is proof that something in the sequence needs another look, no matter what the gauge said.

That is also why good shielding habits extend beyond the torch. Clean base metal, correct prep, and consistent technique all feed the same result, whether you are running a boat hull seam or prepping a benchtop with a proper aluminum cleaner before AC work. Miller’s shielding gas best practices make the same point from the equipment side: gas delivery only works when the whole setup is consistent. The same logic applies when a job demands tighter control, as covered in aerospace TIG welding standards and training.

Start a Cup Log

The single highest-value habit you can build from this chart is a small cup log. Keep a card in the welder or a note on your phone with five fields: material and thickness, cup number, collet body or gas lens, flow rate, and a one-line verdict on the result. After a few months you will have something better than any generic chart, because it will be tuned to your torch, your shop draft, and the joints you actually run.

Start with a compact kit, note what worked, and adjust from evidence instead of memory. For the record, most shops settle into #5, #6, and #8 standard cups plus an #8 and #12 gas lens before buying anything exotic. If you are still dialing in gas purchases alongside those choices, a supplier overview like Airgas welding supplies helps you match cylinder size to real consumption.

Keep the chart taped where you can see it, treat every number in it as a starting point validated by the arc in front of you, and let the puddle make the final call. Do that consistently, and cup size stops being a variable you worry about and becomes the quiet, solved part of every weld you run.

Frequently Asked Questions

What does the number on a TIG cup mean?

The number is the inside diameter of the cup expressed in sixteenths of an inch. A #6 cup is 6/16 inch (9.5 mm), a #8 is 1/2 inch (12.7 mm), and a #12 is 3/4 inch (19.0 mm).

What size TIG cup should I use for most jobs?

A #8 cup (or #8 gas lens) covers the widest range of everyday steel and stainless work in the 100-250 A range. Step up to #10 or #12 for heavier plate and stainless where you need a wider shield, and drop to #5 or #6 for thin material, tight corners and aluminum.

How much argon flow does each cup size need?

A practical rule is about 2-3 CFH per cup size number: a #6 wants roughly 12-18 CFH and a #10 wants 20-30 CFH. Gas lens setups often run the same or slightly lower flow with better coverage, and you should always tune by watching the puddle.

Does a bigger cup always give better shielding?

No. An oversized cup with too much flow becomes turbulent and draws air into the shield, causing porosity. Bigger cups also will not fit tight joints and can make the AC arc on aluminum erratic, so match the cup to the joint and amperage.

When should I use a gas lens instead of a standard collet body?

Use a gas lens when you want smoother laminar flow, longer tungsten stick-out and better coverage on steel, stainless and exotics, typically from #6 upward. Below about #6 a gas lens adds little benefit, and many welders keep plain collet bodies for small cups and aluminum work.

Why is my weld porous even though my gas is on?

Usually the flow is too high for the cup (turbulence), the cup is too small for the weld zone, or a draft is blowing the shield away. Reduce flow, move to a larger cup or gas lens, check for leaks and gaskets, and shield the work area from fan air.

What cup size is best for TIG welding aluminum?

Most welders stay between #5 and #8 on AC aluminum, because the cleaning action and arc stability suffer with very large cups. A #6 gas lens around 12-18 CFH is a common starting point for thin aluminum.

What cup do I need for stainless steel to prevent discoloration?

Use a larger cup such as a #10 or #12 (often with a gas lens) plus adequate flow and a longer post-flow so the weld stays shielded as it cools. Heavy discoloration or sugaring means the shield ended too early or coverage was too narrow.

Do clear Pyrex cups shield as well as ceramic cups?

Yes, when sized and flowed correctly they shield the same way, and their main advantage is visibility for cup walking and tight joints. They are more fragile than alumina and can crack from heat or impact, so handle and store them carefully.