Amperage — What It Is and Why It Matters
Amperage (current, measured in amps) is the primary control for heat input in welding. Higher amperage means more heat into the workpiece, deeper penetration, and a larger weld pool. Lower amperage produces less heat, shallower penetration, and a smaller, more controllable pool.
In constant-current processes (TIG, stick), amperage is set directly on the machine. In constant-voltage processes (MIG), amperage is controlled indirectly through wire feed speed — faster feed increases amperage. Understanding this distinction is fundamental to setting up and troubleshooting any welding process.
Correct amperage selection depends on material type and thickness, joint design, welding position, electrode or wire diameter, and the specific welding process. Too much amperage causes burn-through, excessive penetration, and distortion. Too little causes lack of fusion, poor penetration, and cold lapping. Finding the right amperage is where welding transitions from following a chart to developing real-world judgment.
Frequently Asked Questions
How do I know what amperage to use?
As a starting point, use approximately 1 amp per .001" of material thickness for steel. For example, 1/8" (0.125") steel starts around 125 amps. Then adjust based on joint type, position, and results. Welding charts specific to your machine, wire size, and gas are the best starting reference.
Is amperage the same as heat?
Amperage is the primary contributor to heat input, but heat input also depends on voltage and travel speed. The formula is: Heat Input = (Amps × Volts × 60) / (Travel Speed in inches per minute × 1000). Amperage alone does not tell the full heat story.