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.

What is the Welder Duty Cycle Calculator?

Apply the welder duty cycle inverse-square rule: from a rated duty cycle at rated amps, find the maximum sustainable amps at 100 percent duty, or the safe weld-on minutes per 10-minute window at any higher amperage. Flags overload risk. It runs free in your browser on Gera Tools, with nothing uploaded.

Welder Duty Cycle Calculator

Name: Welder Duty Cycle Calculator
Creator: Gera Tools
License: https://creativecommons.org/licenses/by/4.0/

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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.

Choosing the right machine for a job

Before committing to a welder, check whether its rated duty cycle at the rated amperage actually fits your work. A machine rated 20% at 200 A is designed for short-arc hobby work or maintenance tacking — it can only weld 2 minutes out of every 10 at that output. For a fabrication shop running continuous passes on structural steel at 180–220 A, you need a machine with at least 60% duty cycle at that amperage.

If the nameplate lists only one duty cycle point, use the inverse-square rule to project to other amperages. For example, a machine rated 30% at 200 A has a continuous (100%) amperage of 200 × √(0.30) ≈ 110 A. If you need to weld at 150 A continuously, that machine is not suitable — you would be limited to about 53% duty, which may be workable for slower work but tight for production welding.

The ambient temperature effect

The standard duty cycle rating assumes a 40°C (104°F) ambient temperature. In a hot summer shop or a warm enclosure, the machine’s actual thermal limit is reached sooner because less heat dissipates into the surroundings. As a practical rule:

In a cool workshop (under 25°C), the machine may run slightly above its rated on-time without tripping.
In a hot environment (35–40°C), treat the rated duty cycle as the hard ceiling — you may hit the thermal overload slightly before the full rated on-time expires.
In a very hot environment (over 40°C), reduce the planned on-time by 10–20% to avoid nuisance trips mid-bead.

Thermal overload protection is designed to save the machine, not to penalize the operator — if it trips frequently, it is a reliable signal that the amperage and ambient temperature combination is beyond what the machine can sustain.