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Breaker Size Calculator
Who it's for: Electricians, apprentices, and estimators.
Calculator Inputs
Quick Summary
- Built for: Electricians, apprentices, and estimators.
- Key outputs: Calculated load amps, Required amps with factor, and more.
- Use this page for early planning estimates before final code and manufacturer verification.
Inputs
- Load amps (A) OR load watts (W)
- System voltage (V)
- Phase (single/three)
- Power factor
- Continuous load flag
- Continuous factor (%)
- Motor/HVAC informational flag
- Standard breaker series
Outputs
- Calculated load amps
- Required amps with factor
- Suggested breaker size
- Method explanation
- Planning disclaimer
How this calculator estimates results
- Uses direct load amps input when provided, otherwise converts watts to amps using voltage, phase, and power factor assumptions.
- Applies a configurable continuous-load factor for planning-level breaker demand.
- Selects the smallest breaker in the standard list that meets or exceeds required amps.
Cross-check assumptions with Wire Size Estimator for a more complete planning workflow.
Common ranges and tips
- If both amps and watts are available, compare outputs to catch bad assumptions before field decisions.
- Continuous loads can materially increase required breaker size when planning circuits.
- Review conductor selection with the Wire Size Estimator after selecting a breaker target.
- Final breaker selection must be verified with code, equipment ratings, and project conditions.
Related Calculators
FAQ
Yes. If load amps is provided, the calculator uses that value directly and bypasses the watts-to-amps conversion path.
Continuous-load factors increase the required planning amperage so that sustained current assumptions are reflected in the suggested breaker range.
Not in this MVP version. It is informational only; motor and HVAC-specific protective-device rules still require dedicated code checks.
No. Use this as a planning estimate only and verify final breaker and conductor sizing with adopted code and manufacturer documentation.
Disclaimer: Use results for planning only. Final design and installation decisions must follow local code and manufacturer documentation.
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