How to Weld Carbon Steel
Published October 3, 2026 · Built by Jeremy Panasuk
In the charts this site actually cites, the metal is called steel or mild steel, not a carbon grade. Miller’s solid-wire parameter page is a steel example. The farm chart’s thickness cells are mild steel. The calculator’s MIG tab does not ask for a carbon percentage, and this page will not invent one. “Carbon steel,” for a planning weld on this site, means that steel path: solid wire or a stick electrode on metal that is not stainless and not aluminum. If the steel is coated, stop and use the galvanized page. If it is rusty, the stick condition input changes, which is cleaning.
Miller’s published 1/8 inch example
Miller states a solid-wire rule of 1 amp for each .001 inch of steel. The worked example is 1/8 inch, written as .125 inch, at 125 amps. Wire speed on that page is amps times a multiplier that depends on diameter. At the 125 amp example, .030 inch wire uses 2 inches per amp, which is 250 inches per minute, and the published window for .030 inch wire is 40–145 amps. Those figures are the chart. The 1/8 inch welder page stays with that chart and with the farm cells. This page asks a different question: what the MIG function on this site returns if you type the same thickness.
Worked example: 125 mils on the MIG tab
One-eighth inch is 125 mils. On the MIG tab, enter 125 and leave shielding on 75/25 argon/CO2, the clean mild-steel choice. Wire size is chosen by thickness bands: under 78 mils is .023 inch, under 188 mils is .030 inch. 125 falls in the .030 band. Amps are 125 times 0.8, then rounded to the nearest 5. That product is 100, and 100 is already a multiple of 5, so the amp start is 100. The display adds 15 percent and rounds, which is 115. The line you see is .030 inch wire at 100–115 amps. Wire speed uses a multiplier of 2.0 inches per amp for .030 wire: 100 times 2 is 200 inches per minute, and 10 percent more is 220. Gas flow prints as 20–25 cubic feet per hour. The power line says a 120 volt machine is OK, because 125 mils is under the 188-mil step that flips the label to 220 volts.
Set the two results side by side and do not blend them.
| Miller’s solid-wire example | This site’s MIG function | |
|---|---|---|
| Input | .125 in steel, the published example | 125 mils, 75/25 shielding |
| Wire | .030 in is one of the diameters in the example | .030 in, because 125 is under 188 mils |
| Amps | 125 A, inside a 40–145 A window for .030 in | 100–115 A |
| Wire speed | 2 in per amp at 125 A, which is 250 ipm | 2.0 in per amp at 100 A, which is 200–220 ipm |
Both use a “2 inches per amp” idea for .030 wire. They do not use it at the same amperage, so the wire-speed results differ by the amp difference: 250 inches per minute at Miller’s 125 amps, versus 200 at the function’s 100 amp start. The function is a coarser band. Miller’s page is the worked example with a stated 125 amp point. If you are matching that page, set 125 amps and 250 inches per minute and then tune. If you are asking what this website’s button does, the answer is 100–115 amps and 200–220 inches per minute. Quoting one and attributing it to the other is a citation error, not a weld.
The function’s note on the result assumes mild steel, short-circuit transfer, and a joint you can reach flat or horizontal. It tells you to listen for a steady crackle. That listening instruction is not a measured voltage. This page does not add a voltage, because the function does not output one.
Stick is available, and it is not this MIG result
Carbon steel is also welded with stick. The stick tab at 250 mils, which is 1/4 inch, is the example on the cleaning page: 1/8 inch E7018 at 90–140 amps when the metal is clean. At 125 mils the same stick function does something less intuitive, a 1/16 inch rod, which is walked through on how to weld. Do not paste the MIG tab’s 100–115 amps onto a 7018 rod. Process first, then the tab that matches it.
A common mistake
The mistake is one rule for every dial. “One amp per thousandth” is Miller’s solid-wire statement, and it produces 125 amps at 1/8 inch. This MIG function uses 0.8 amp per mil inside the .030 band and then rounds to a 5-amp step, and it produces 100. A beginner who sets the machine to 125 because of Miller, and sets wire speed to 200 because of the button, has mixed the two systems. Pick one source for the pass you are about to run, write down its amps and its wire speed together, and confirm on scrap of the same thickness.
Limits
Nothing here is a carbon-equivalent, a preheat temperature, or a filler classification beyond the wire diameter the function prints. If the steel is high-carbon, unknown, thick enough to need a qualified procedure, or a load-bearing joint, those decisions are outside this chart. Machine class for 1/4 inch plate is the 1/4 inch page. The 120 volt label on this 125-mil run only means the function’s thickness step did not flip. It is not a circuit calculation.
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Frequently asked questions
What is Miller’s published example for 1/8 inch steel?
Miller’s solid-wire page uses 1 amp per .001 inch. The worked example is 1/8 inch, .125 inch, at 125 amps. At that amperage, .030 inch wire is listed at 2 inches per amp, which is 250 inches per minute, inside a 40–145 amp window.
What does this MIG tab return for 125 mils?
Wire diameter .030 inch, because 125 is under 188 mils. Amps are 125 times 0.8, rounded to the nearest 5, which is 100, shown as 100–115. Wire speed is 100 times 2.0, which is 200–220 inches per minute. Shielding on the clean-steel choice is 75/25 argon/CO2. The power line says a 120 volt machine is OK.
Does carbon steel get a separate chart on this site?
No. The sources this site uses say steel or mild steel. The calculator’s steel path is that metal. There is no separate carbon-percentage input, and this page does not invent one.
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Compiled with AI assistance from the sources below. Spot an error? Email [email protected].
Sources
- Miller Electric, “MIG Welding: Setting the Correct Parameters.” https://www.millerwelds.com/en-US/resources/knowledge-hub/mig-welding/how-to/mig-welding-setting-the-correct-parameters. Accessed October 3, 2026.
- Miller Electric, “Welding on the Farm: Selecting a Welding Unit for the Farm or Ranch,” hosted by Ohio State University Marion. https://marion.osu.edu/sites/marion/files/imce/Welding%20on%20the%20Farm.pdf. Accessed October 3, 2026.