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What Is Arc Welding?

Published October 3, 2026 · Built by Jeremy Panasuk

“Arc welding” is the family name, not a setting. OSHA’s fact sheet on welding fume splits welding into fusion (heat alone) and pressure (heat and pressure). It then names three types of fusion welding: electric arc, gas, and thermit. Electric arc welding, OSHA says, is the most widely used, and it employs an electric arc to melt the base and filler metals. Gas welding uses a flame, usually from acetylene. Thermit welding uses a chemical reaction instead of gas or current. This page stays with the electric-arc branch, because that is the branch the calculator can put a number on. Gas and thermit are real processes. They are not tabs on the thickness calculator.

The arc processes OSHA names, in fume order

The same fact sheet lists arc welding types in order of decreasing fume production, and then describes four of them. Flux-cored arc welding uses a flux-cored filler. Shielded metal arc welding, the stick process, uses an electrode that supplies both flux and filler. Gas metal arc welding, called MIG on this site, uses a consumable electrode and an external gas shield. Gas tungsten arc welding, called TIG here, uses a non-consumable electrode and an externally supplied inert gas, and OSHA describes it as the one with the superior finish.

That order is about fume, not about which process is “better,” and it is not a shopping list. The calculator sizes three of those four: stick, MIG, and TIG. It does not have a flux-cored tab. Flux-cored amps on this site, where they appear, are cells copied from the farm chart, not a fourth function. Sheet-metal process choice between MIG and TIG is a separate page, MIG or TIG for sheet metal.

BLS describes the same idea in occupational terms: in arc welding, workers use machinery that produces electrical currents to create heat and bond metals, and they choose a process based on factors such as the types of metals being joined. Choosing the process is the step before any amp.

One thickness, three published figures

Take 1/8 inch of steel, which is .125 inch, or 125 mils. Miller’s solid-wire MIG page uses that thickness as the worked example of its rule, 1 amp for each .001 inch, and states the result as 125 amps. The farm chart’s 1/8 inch mild-steel cells, quoted on the 1/8 inch welder page, are a different set: stick E6013 at 80–130 amps, flux-cored at 140–155 amps, and TIG at 95–130 amps. None of those is “the arc welding amp.” Each is a process.

Worked example: the TIG tab at 125 mils of steel

Open the TIG tab. Enter 125. Leave the material on mild steel. The function uses a factor of 1.0, so the midpoint is 125 amps. It then shows 80 to 120 percent of that midpoint, rounded, which is 100–150 amps. Polarity is DCEN. Tungsten and filler both print as 3/32 inch, because 125 mils clears the function’s 94-mil tungsten step and its 125-mil filler step.

Read that beside the other two sources, not instead of them. The calculator’s TIG window is 100–150 amps. The farm chart’s TIG cell is 95–130 amps. Miller’s 125 amps is the solid-wire MIG example, and it happens to sit inside both TIG windows without being a TIG setting. If you came here for a single number to write on a machine, the sources do not give you one. They give you a process first.

A common mistake

The mistake is hearing “arc welder” and typing one amperage. A 125 amp MIG example, a 95–130 amp TIG cell, and a 100–150 amp calculator band can all be true for the same 1/8 inch of steel. They answer different questions. Flux-cored, on the farm chart, is 140–155 amps for that thickness, which is above Miller’s 125. Using the MIG example on a stick joint, or the stick cell on TIG, is how the bead either sits on top or blows through.

Limits

OSHA’s fact sheet is about fume and gases, not about a procedure for your joint. Acute exposure can irritate eyes, nose, and throat and can cause dizziness and nausea, and OSHA says workers who get those symptoms should leave, get fresh air, and obtain medical attention. Shielding gases can displace oxygen, particularly in a confined space. Nothing on this page weakens that. Arc welding still needs the ventilation and coating-removal steps in how to weld galvanized steel safely when the metal is coated, and a clean joint when it is not, which is how to clean metal before welding. A code weld, a pressure part, or a metal you cannot identify is a qualified procedure, not a calculator result.

Frequently asked questions

What does OSHA call arc welding?

OSHA’s welding fact sheet says fusion welding is heat alone, and that there are three types of fusion welding: electric arc, gas, and thermit. Electric arc welding is the most widely used. It employs an electric arc to melt the base and filler metals.

Which arc processes does this calculator size?

The calculator has tabs for GTAW (TIG), GMAW (MIG), and SMAW (stick), plus duty cycle. OSHA also names flux-cored arc welding. Gas welding and thermit welding are on OSHA’s fusion list and are not in the calculator.

Is there one amp number for 1/8 inch steel?

No. Miller’s solid-wire MIG example is 125 amps at .125 inch. The farm chart’s TIG cell for 1/8 inch is 95–130 amps. This site’s TIG function, given 125 mils of steel, returns 100–150 amps.

Compiled with AI assistance from the sources below. Spot an error? Email [email protected].

Sources