What Is a Welding Duty Cycle Derating Calculator?
Duty cycle is the percentage of a 10-minute period a welding power source can run continuously at its rated amperage before it needs to cool down to avoid overheating. This calculator uses the standard constant-I²t derating formula to find the maximum amperage safe for any desired duty cycle, based on the machine's nameplate rating.
This is the same relationship welding equipment manufacturers use to publish duty-cycle-versus-amperage charts, made interactive so you can plug in your own numbers.
How to Read Your Results
Max Amperage at Desired Duty Cycle
The highest amperage you can run at your chosen duty cycle without exceeding the power source's thermal limits.
Max Amperage at 100% Duty Cycle
The continuous-rated amperage — what the machine can deliver welding non-stop, which is always lower than its short-duty-cycle rating.
Change vs. Rated Amperage
How much higher or lower the derated amperage is compared with the nameplate rating, as a percentage.
Real-World Example
A welder is rated 250A at 60% duty cycle. A production job needs the arc on almost continuously, so the operator plans for 100% duty cycle.
| Item | Value |
|---|---|
| Rated amperage / duty cycle | 250 A @ 60% |
| Desired duty cycle | 100% |
| Derated amperage | ≈194 A |
Running continuously, the machine must be limited to about 194A instead of its 250A short-duty-cycle rating — roughly a 22% reduction — to avoid overheating.
Tips for Managing Duty Cycle
- Higher duty cycle always means lower safe amperage, and vice versa — the trade-off follows a square-root curve, not a straight line.
- Ambient temperature and ventilation affect real-world thermal limits; treat this as a starting estimate.
- Check the manufacturer's actual derating chart when precision matters, since some machines don't follow the ideal I²t curve exactly.
- Running above the safe amperage for your duty cycle can trip thermal overload protection or shorten power source life.
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Last updated: August 2026 · Reviewed by: Simple Calculator Tools Editorial Team