Welding and Metalwork Calculators
Welder duty cycle calculator.
Enter the rated amps and duty cycle from the rating plate to see welding and rest minutes per 10, then estimate the duty cycle at the amps you will really run. Runs in your browser; nothing is sent or stored.
Inputs
Result
Fill the form and press Calculate.
Answer first. Duty cycle is a percentage of a 10-minute period. Miller Electric explains that dividing the rating by 10 gives the minutes you can weld continuously before the machine must cool: a machine rated 30 percent at 215 amps can weld for 3 minutes and then needs 7 minutes to cool at that current.
Worked example
A welder rated 40 percent at 250 A. At 250 A you get 4 minutes of welding and 6 minutes of cooling per 10. Welding at 200 A, the estimate is 40 x (250 / 200)^2 = 62.5 percent, about 6.3 minutes in 10. At 150 A the formula gives 111 percent, so it is capped at 100 percent (continuous), and the highest current it estimates as continuous is 250 x sqrt(0.40) = 158 A.
How it works
Definition. Miller Electric's knowledge hub describes duty cycle as expressed as a percentage over a 10-minute period, and says high amperage settings often mean a shorter duty cycle. Its example is a Millermatic 211 PRO rated at 30 percent at 215 A.
The estimate at another current. Heat in the machine's windings and electronics rises with the square of the current, so this tool estimates new duty = rated duty x (rated amps / amps used)^2, capped at 100 percent. That is an engineering approximation, not a figure from a manufacturer, and real machines can differ in either direction. If your manual has a duty cycle versus amps chart, use that instead.
What changes the real number. A rating applies to one current and input voltage (Miller's example is 30 percent at 215 A on 240 V), so read the rating plate for the supply you are using. If the machine overheats or a thermal overload trips, stop welding and let it cool.
Safety. Welding produces arc radiation, fumes, sparks and burns. Use a proper welding helmet, gloves and flame-resistant clothing, ventilate or extract fumes, and remove flammables from the area. This is a planning aid, not a welding procedure, engineering design or professional advice.
Sources
- Duty Cycle: What It Is and Why It's Important (Miller Electric) (opened 2026-10-15)
The 10-minute definition and the 215 A example are from the Miller Electric page. The squared-current scaling is a stated approximation.
FAQ
What does 30% duty cycle mean on a welder?
Out of every 10 minutes you can weld for 3 minutes at the rated amps, then the machine needs about 7 minutes to cool.
How many minutes can I weld at 60% duty cycle?
6 minutes in every 10 at the rated current, with 4 minutes of cooling.
Does a lower amperage give a higher duty cycle?
Yes. Miller notes that high amperage settings often mean a shorter duty cycle. This tool estimates the change with a squared-current rule, capped at 100 percent.
Is the estimate exact?
No. It is an approximation. The duty cycle chart in your welder manual, if it has one, overrides the estimate.
Can I weld above the rated amps?
The tool will estimate a shorter duty cycle, but running above the rating plate current can exceed what the machine is designed for. Check the maximum output in the manual.