Circuit Breaker Sizing Calculator: NEC 125% Rule for Continuous Loads

Circuit Breaker Sizing Calculator

NEC 125% rule for continuous loads — get the next standard breaker size for any circuit.

NEC 240.6 standard circuit breaker sizes chart — PES Supply

By Jennifer Kirstens · August 30, 2026 · 6 min read

Quick answer

Breaker sizing: 125% of continuous load, next standard size up (NEC 240.4(B)) up to 800A. A 16A continuous load → 20A breaker. Calculator below.

Circuit Breaker Sizing Calculator (NEC 125% Rule)

Sizes the breaker for continuous + non-continuous loads per NEC 210.20(A) and 215.3, and picks a matching copper AWG.
References: NEC 210.20(A) (branch OCP), 215.3 (feeder OCP), 240.4 (conductor protection), 240.6(A) (standard sizes).
Related: How to Size a Circuit Breaker
Related PES calculators: Duct Sizing · Wire Size · Breaker Sizing

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