Breaker Size Calculator - NEC

NEC 240 overcurrent protection & breaker sizing for electricians. Works offline.

NEC breaker size calculator for electricians, apprentices, and electrical engineers. Size overcurrent protection devices per NEC Article 240, with automatic continuous load adjustment, next-size-up rule, small conductor limits, and wire-breaker coordination. Works 100% offline on the job site.

Whether you're sizing a breaker for a 40A continuous lighting load, selecting overcurrent protection for an AC unit, or checking if a 14 AWG conductor needs a 15A breaker limit, this calculator gives you accurate NEC-compliant results in seconds. Use it as your go-to breaker sizing reference — from load analysis to conductor coordination.

BREAKER SIZE CALCULATOR FEATURES:
• All 36 standard overcurrent device ratings from 15A to 6000A per NEC 240.6(A)
• Automatic next-size-up breaker selection
• Continuous load 125% multiplier per NEC 210.20(A)
• Three load types: General, AC/Refrigeration (175%), Welder (200%)
• Small conductor protection limits per NEC 240.4(D): 14 AWG max 15A, 12 AWG max 20A, 10 AWG max 30A
• Wire-breaker coordination check per NEC 240.4
• Recommended conductor size from NEC Table 310.16 (75°C column)
• Copper and aluminum conductor support
• 6 voltage presets: 120V, 208V, 240V, 277V, 480V, 600V
• Single-phase and three-phase support
• NEC article references for every calculation result

NEC REFERENCES INCLUDED:
• NEC 240.6(A) — Standard overcurrent device ratings
• NEC 210.20(A) — Continuous load 125% rule
• NEC 240.4(B) — Next standard size up rule
• NEC 240.4(D) — Small conductor protection limits
• NEC 240.4 — Overcurrent protection of conductors
• NEC Table 310.16 — Conductor ampacity at 75°C

LOAD TYPE SUPPORT:
• General loads — 100% non-continuous, 125% continuous per NEC 210.20(A)
• AC/Refrigeration — 175% per NEC Article 440
• Welder — 200% per NEC 630.12

CALCULATION RESULTS INCLUDE:
• Recommended breaker size (standard rating per NEC 240.6(A))
• Adjusted load amps with multiplier explanation
• Recommended conductor size with ampacity from Table 310.16
• Breaker-to-wire ampacity verification
• Small conductor warnings when applicable
• Complete NEC article references for each result

PRO FEATURES (one-time purchase):
• No ads — clean interface for professionals
• Save breaker calculation history with labels
• Export calculations as PDF reports for permits and records
• Dark theme support

HOW THE BREAKER SIZE CALCULATOR WORKS:
1. Select load type (General, AC/Refrigeration, or Welder)
2. Enter load amps
3. Toggle continuous load if applicable
4. Select voltage and phase
5. Choose conductor material (copper or aluminum)
6. Get breaker size, wire recommendation, and NEC references instantly

BUILT FOR ELECTRICIANS ON THE JOB SITE:
This breaker size calculator is designed by electricians, for electricians. Enter your load parameters, get the correct breaker size and wire recommendation instantly — no complicated menus or unnecessary features. One-hand operation, instant results.

PERFECT FOR:
• Licensed electricians sizing breakers daily
• Electrical apprentices studying for journeyman exams
• Electrical engineers and designers
• Electrical contractors bidding jobs
• NEC code exam preparation
• Journeyman and master electrician exam study

OFFLINE & PRIVACY:
• Works 100% offline — no internet needed on the job site
• No account required
• No data collection — your calculations stay on your device

Simplify your breaker sizing on the job site.