Most welders used in home shops and small fabrication settings draw between 20 and 50 amps from a wall circuit, depending on the input voltage and welding output. The welding output itself, which is what actually melts the metal, typically ranges from 30 amps for thin sheet metal work up to 300 amps or more for thick structural steel. Understanding both numbers matters because one determines whether your electrical panel can handle the machine, and the other determines what you can actually weld.
Output Amperage by Welding Process
The amperage a welder puts into the metal varies by process, material thickness, and the type of joint you’re making. Here’s a practical breakdown of the three most common processes.
MIG welding (wire-feed) is the most popular choice for home shops and light fabrication. Small 120-volt MIG welders typically output 30 to 140 amps, which handles sheet metal up to about 3/16-inch steel. Larger 240-volt MIG machines push 30 to 250 amps or more, letting you weld 3/8-inch steel and beyond.
Stick welding (SMAW) uses consumable electrode rods and is common for structural work, repairs, and outdoor jobs. A basic stick welder runs 40 to 225 amps. Thinner rods (1/16 or 5/64 inch) run at the low end, while 5/32-inch and 3/16-inch rods need 120 to 225 amps. The general rule is simple: thinner metal and smaller rods need fewer amps, thicker metal and larger rods need more.
TIG welding uses a non-consumable tungsten electrode and is favored for precise, clean work on stainless steel, aluminum, and thin materials. TIG welding on thin aluminum or stainless might use as little as 10 to 15 amps. Welding 1/4-inch aluminum can require 250 amps or more. TIG generally uses lower amperage than stick or MIG for the same material thickness because the arc is more focused.
Input Amperage: What Your Circuit Needs
Output amperage is what melts metal. Input amperage is what the machine pulls from your electrical panel, and this is the number that determines whether you need to upgrade your wiring. A welder’s input draw is always higher than you might expect because the machine loses some energy as heat during the conversion process.
A 120-volt welder (capable of up to about 140 amps of welding output) needs a minimum 20-amp breaker, with 30 amps recommended. A 208 to 230-volt welder (outputting up to about 180 amps) requires at least a 30-amp breaker, with 50 amps recommended. Welding at 200 amps output or more requires at least a 50-amp breaker and dedicated wiring, similar to what an electric range or dryer uses.
If your garage or shop only has standard 120-volt, 15-amp outlets, you’ll trip the breaker constantly with even a small welder. At minimum, you need a dedicated 20-amp 120-volt circuit. For anything beyond light-duty work, a 240-volt outlet on a 50-amp circuit gives you the most flexibility.
How Material Thickness Affects Amperage
A rough starting point for mild steel with stick welding is 1 amp per thousandth of an inch of material thickness. So 1/8-inch steel (0.125 inches) needs roughly 125 amps. That’s a ballpark, not a rule, and it varies with joint type, electrode choice, and position.
For MIG welding, the relationship is similar but the wire diameter and voltage setting also play a role. Thin 18-gauge sheet metal (about 0.048 inches) might need only 30 to 50 amps with a small wire. Quarter-inch plate could need 180 to 200 amps with thicker wire. Aluminum requires more amperage than steel of the same thickness because it conducts heat away from the weld pool faster.
Every welder’s manual includes a settings chart for its specific machine. Those charts, along with test welds on scrap material, are far more reliable than generic guidelines.
Duty Cycle and Why It Matters
A welder’s amperage rating always comes paired with a duty cycle, which tells you how long the machine can run at that amperage before it needs to cool down. Duty cycle is measured as a percentage of a 10-minute window. A machine rated at 30% duty cycle at 215 amps can weld continuously for 3 minutes, then needs 7 minutes of cooling.
The relationship between amperage and duty cycle is inverse: the higher the amperage you dial in, the shorter the duty cycle. Most home-shop welders running at maximum output have duty cycles between 20% and 40%. Drop the amperage to 60% or 70% of the machine’s maximum, and the duty cycle often climbs to 60% or higher. For most hobbyist projects, this isn’t an issue because you’re welding in short bursts, tacking pieces together and repositioning between runs.
If you’re planning long, continuous welds on heavy material, you need either a machine with a higher duty cycle rating at your target amperage, or you’ll have to plan cooling breaks into your workflow. Running a machine past its duty cycle triggers a thermal overload shutoff that protects the internals, but repeatedly overheating the machine shortens its lifespan.
Inverter vs. Transformer Power Draw
Older transformer-based welders are heavy, simple machines that convert wall power to welding power using copper coils. They work reliably but draw more electricity for the same welding output. Modern inverter welders use electronic circuitry to convert power more efficiently, meaning they pull fewer amps from your wall circuit to deliver the same welding amperage. An inverter welder that outputs 200 amps might draw noticeably less input current than a transformer machine at the same setting.
This efficiency difference has a practical benefit: inverter welders are more likely to run on existing household circuits without upgrades. A 120-volt inverter MIG welder can often operate on a 20-amp circuit that would trip instantly with an old transformer unit at similar output. Inverter machines also weigh 30 to 70 pounds less than their transformer equivalents, which matters if you’re moving the welder around a shop or loading it into a truck.
Choosing the Right Amperage for Your Work
If you’re welding auto body panels, exhaust systems, or thin-wall tubing, a 120-volt machine outputting up to 140 amps handles most of the work. For general fabrication, trailer repairs, or projects involving 1/4-inch steel and thicker, you’ll want a 240-volt machine capable of at least 200 amps of output.
Buy more amperage than you think you need. A machine rated at 250 amps that you run at 150 amps will have a longer duty cycle, run cooler, and last longer than a 180-amp machine pushed to its limit on the same job. The electrical infrastructure is the harder constraint. If you’re setting up a shop, installing a 240-volt, 50-amp circuit from the start saves you from paying an electrician twice.