What is welding duty cycle?

Duty cycle is the percentage of a 10-minute window a welder can run at a given amperage without overheating. A 60 percent duty cycle at 200 A means six minutes of welding then four minutes of cooling per ten minutes.

What formula converts duty cycle between amperages?

The inverse-square rule: new duty cycle = rated duty cycle x (rated amps / new amps) squared. Higher current produces more heat, so allowable on-time falls with the square of the current ratio.

How do I find the amperage for 100 percent duty cycle?

Rearrange the rule: max continuous amps = rated amps x sqrt(rated duty cycle / 100). At that current the welder can run indefinitely without exceeding its thermal limit.

What happens if I exceed the duty cycle?

The machine's thermal overload protection trips and output cuts out until it cools, or in unprotected machines the transformer or inverter can be damaged. The tool flags when your chosen amperage gives less than a usable on-time.

Is the 10-minute window standard?

Yes. NEMA and IEC 60974 both define duty cycle over a 10-minute test period at 40 degrees C. A 40 percent duty cycle therefore means four minutes welding and six minutes idle within each ten minutes.

Welder Duty Cycle Calculator

A welder’s duty cycle tells you how long it can run before it must cool. Push the amperage above its rating and the safe on-time drops sharply because heating rises with the square of the current. This calculator applies the standard inverse-square rule so you know exactly how many minutes per ten you can weld at any amperage.

How it works

The governing relationship between current and allowable duty cycle is:

new duty cycle = rated duty cycle × (rated amps / new amps)²
on-time min    = (allowable duty cycle / 100) × 10
max continuous amps = rated amps × √(rated duty cycle / 100)

Because heat is proportional to current squared, doubling the current would cut the allowable duty cycle to a quarter. The on-time is simply that duty cycle applied to the standard 10-minute NEMA/IEC window.

Example and notes

A welder rated 60 percent at 200 A run at 250 A gives 60 x (200/250)squared = 38.4 percent, or about 3.8 minutes of welding per 10-minute window. The same machine can run continuously (100 percent) at 200 x sqrt(0.6) = 155 A. Always weld below your machine’s continuous amperage for long passes, and remember the ratings assume 40 degrees C ambient; a hot shop lowers the real duty cycle.