Your files stay on your device

# Circuit breaker size calculator

Pick a standard breaker rating for your circuit and see each coordination rule checked with a pass or fail and the reason.

Enter the design current and cable capacity to size the breaker.

The multipliers here are starting points from common practice, such as 250 percent of full-load current for motors and 125 percent for continuous loads. Real coordination work also considers upstream devices, selectivity between breakers, ambient derating already inside Iz, and the local code text, which wins every time it differs from this page. Nothing you type leaves the tab.
Options

## More unit & math tools

- [4-20 mA scaling](/converters/4-20ma-scaling-calculator)
- [555 timer calculator](/converters/555-timer-calculator)
- [Unit converter](/converters/units)
[All unit & math tools](/converters)

Was this tool useful?
YesNo

---

Canonical HTML: https://nutter.tools/converters/circuit-breaker-size-calculator
Markdown version: https://nutter.tools/converters/circuit-breaker-size-calculator.md
Plain-text version: https://nutter.tools/converters/circuit-breaker-size-calculator.txt
Agent index: https://nutter.tools/llms.txt