Why does the breaker size divide current by 0.8?

Electrical code (like the NEC in the US) requires breakers on continuous loads to be sized so the load doesn't exceed 80% of the breaker's rating, this 80% continuous-load derating rule prevents nuisance tripping and overheating.

Why is the recommended breaker size rounded up?

Breakers only come in standard sizes (15A, 20A, 25A, 30A, and so on). The calculator rounds your calculated requirement up to the next standard size since you can't buy a breaker at an arbitrary amperage.

Electrical Load Calculator

Calculate current draw and recommended breaker size from connected electrical load.

How this is calculated

Current = watts ÷ voltage. Breaker size ≥ current ÷ 0.8, rounded up to the next standard size

Assumptions used in this calculation

Not a substitute for code: Uses the standard 80% continuous-load rule as a guideline, always follow local electrical code and consult a licensed electrician.

About this calculator

Calculates current draw from total connected wattage and voltage, then recommends a standard breaker size using the 80% continuous-load rule.

Worked example

2400W at 120V

Result: 20A current, 25A recommended breaker

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Frequently asked questions

Why does the breaker size divide current by 0.8?

Why is the recommended breaker size rounded up?

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