Welding Amperage Calculator
Estimate a starting welding amperage from material thickness using the one-amp-per-thousandth rule, adjusted for the metal you are joining.
How it works
Amperage ≈ thickness(in) × 1000 × material factor (steel 1.0 · stainless 0.9 · aluminum 1.5) · Working range = ±10%
The classic shop rule is roughly one amp of current for every 0.001 inch (one thousandth) of mild-steel thickness — a 1/8-inch (0.125 in) plate lands near 125 amps. Stainless needs slightly less current because it holds heat, while aluminum needs markedly more because it conducts heat away fast. Treat the number as a starting point: joint fit-up, position, travel speed and electrode type all shift the ideal setting, so always confirm against your machine chart or a test coupon.
Worked example
For 1/4-inch (0.25 in) mild steel: 0.25 × 1000 × 1.0 = 250 A. Dial in around 250 amps and adjust within 225–275 A until the bead ties in without burning through.
Frequently asked questions
Does this work for MIG, TIG and stick?
It gives a reasonable starting amperage for all three on carbon steel, but each process and electrode has its own optimal window. Use it as an opening setting, then tune to the puddle and to the manufacturer’s chart for your specific wire or rod.
Why does aluminum need more amperage?
Aluminum conducts heat roughly three times faster than steel, so heat escapes the weld zone quickly. You need extra current (and often preheat on thick sections) to build and hold a puddle.
What if I burn through the metal?
Burn-through means too much heat input — lower the amperage, speed up your travel, or use a smaller electrode. On thin sheet, dropping to the low end of the range and moving faster usually fixes it.
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This calculator is for educational purposes. Double-check important results before acting on them.