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.

Welding Amperage by Material Thickness

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 × material × position
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.

Example and notes

Eighth-inch carbon steel (0.125 inch) welded with stick in the flat position lands around 110 to 145 amps, centered near 125. Switch the same joint to aluminium and the range climbs by about a third; drop to a vertical TIG weld on stainless and it falls well below the steel baseline. Always treat the result as a first dial-in: run a test bead on scrap and nudge the current up for deeper penetration or down if you are blowing through, and follow the procedure spec for any critical work.