What is the 1 amp per thousandth rule?

A common shop rule of thumb sets the welding current to roughly one amp for every thousandth of an inch of carbon steel thickness in the flat position. So eighth-inch plate, about 125 thousandths, starts near 125 amps. It is a starting point, not an exact figure, and is adjusted for process and material.

Why does aluminium need more amperage?

Aluminium conducts heat far better than steel, so heat drains away from the weld quickly and you need substantially more current to reach and hold a molten puddle. This tool applies roughly a thirty percent increase for aluminium compared with the same thickness of carbon steel.

Does TIG use less current than stick or MIG?

For the same thickness, TIG generally runs at lower current because it deposits filler more slowly and is used on thinner, more controlled work, while MIG runs slightly hotter for good penetration. The tool lowers the TIG estimate and nudges the MIG estimate up relative to the stick baseline.

Why does welding position change the amperage?

Out-of-position welds such as vertical and overhead need a slightly cooler, more controllable puddle so the molten metal does not sag or fall. Reducing the current a little helps you keep control, which is why the tool trims the estimate for those positions compared with flat welding.

Should I trust this for a critical or coded weld?

No. These are rough starting numbers for general fabrication. For structural, pressure, or coded work, follow the welding procedure specification and the electrode or wire manufacturer's published amperage range, and qualify your settings with test coupons.

What is the Welding Amperage by Material Thickness?

Estimates a starting welding amperage range from material thickness using the 1 amp per 0.001 inch rule, then adjusts for process (stick, MIG, TIG), base material (carbon steel, stainless, aluminium), and welding position. Outputs a practical minimum to maximum amp range. Runs in your browser. It runs free in your browser on Gera Tools, with nothing uploaded.

Welding Amperage by Material Thickness

Name: Welding Amperage by Material Thickness
Creator: Gera Tools
License: https://creativecommons.org/licenses/by/4.0/

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Setting the right amperage is the difference between a strong weld, a cold lap, and a burn-through. This calculator gives a sensible starting amperage range from the metal thickness, then adjusts it for your process, base material, and position so you spend less time guessing on scrap.

How it works

The starting point is the classic rule that carbon steel needs about one amp for every thousandth of an inch of thickness in the flat position. From that center value the tool applies multipliers and builds a practical range:

base amps = thickness(in) × 1000
adjusted  = base × process_factor × material_factor × position_factor
range     = adjusted × 0.85  to  adjusted × 1.15

Stick welding is the baseline, MIG runs a little hotter, and TIG a little cooler. Stainless runs cooler than carbon steel because it holds heat, while aluminium needs far more current because it sheds heat fast. Vertical and overhead positions take slightly less current for puddle control.

Adjustment factors at a glance

Variable	Direction	Why
MIG vs stick	+5–10%	Continuous wire feed deposits faster, needs more heat
TIG vs stick	−10–20%	Slower travel, more control, often on thinner material
Aluminium vs carbon steel	+25–35%	High thermal conductivity drains heat from the puddle
Stainless vs carbon steel	−5–10%	Low thermal conductivity retains heat; excess warps and sensitises
Vertical/overhead vs flat	−10–15%	Gravity pulls the puddle; lower current for better control

Worked example

For eighth-inch (0.125 in) carbon steel in the flat position:

Base amps: 0.125 × 1000 = 125 A (center)
Range: 125 × 0.85 to 125 × 1.15 = 106–144 A

Switch the same thickness to aluminium TIG: base × TIG factor (~0.85) × aluminium factor (~1.30) gives a center near 138 A, range roughly 117–159 A — substantially hotter despite being TIG, because aluminium sheds heat so aggressively.

Now try stainless vertical stick: center near 125 × 0.95 (stainless) × 0.88 (vertical) ≈ 104 A, range roughly 88–120 A — cooler to avoid warping and avoid sensitisation of the heat-affected zone.

What to do after getting the estimate

The calculator gives you a start point; dialling in the actual setting always takes a test bead on scrap:

Too cold (cold lap): the bead sits on top of the base metal with a raised edge, no fusion. Increase current 5–10 A and re-test.
Too hot (burn-through or undercut): the arc blows through or cuts a groove along the weld edge. Reduce current or increase travel speed.
Spatter (MIG): may be too low voltage relative to wire speed rather than a pure amperage issue. Adjust the voltage/wire-speed ratio first.
For electrode amperage limits, also check the electrode manufacturer’s data sheet. Each electrode diameter has its own rated amp range that can override the thickness rule.

Never rely on these estimates for structural, pressure, or coded welds — use the tested amperage range from your Welding Procedure Specification (WPS) and qualify with test coupons per the relevant code (AWS D1.1, ASME IX, etc.).