Standard Breaker Sizes NEC & Fuse Ratings
Free online tool • 2026 NEC Compliant
NEC Table 240.6(A) defines standard overcurrent protection device (breaker and fuse) ratings. When calculations result in non-standard ratings, the code generally allows rounding up to the next standard size. Use the breaker sizing calculator below, and reference the official standard amperage charts on this page.
Recommended Sizing
NEC Standard SizeBreaker Type: Standard Inverse-Time
NEC Reference Note: 125% multiplier applied for continuous loads per NEC 210.20(A).
How to Use This Calculator
Calculate circuit load
Sum continuous loads at 125% and non-continuous loads at 100%.
Find required ampacity
Select a conductor with an ampacity rating matching or exceeding the calculated load.
Compare to standard sizes
If the conductor ampacity does not match a standard size under 800A, round up to the next standard breaker rating.
Frequently Asked Questions
What are standard breaker sizes?
Per NEC 240.6(A), standard inverse-time circuit breaker ratings are 15, 20, 25, 30, 35, 40, 45, 50, 60, 70, 80, 90, 100, 110, 125, 150, 175, 200, 225, 250, 300, 350, 400, 450, 500, 600, 700, 800, 1000, 1200, 1600, 2000, 2500, 3000, 4000, 5000, and 6000 Amps. Additional standard fuse ratings include 1, 3, 6, and 10 Amps.
Can I round up to the next standard breaker size?
Yes. Under NEC 240.4(B), you can use the next standard overcurrent device rating (rounding up) if the calculated conductor ampacity does not correspond to a standard size, provided the rating does not exceed 800 amps and the circuit is not a multioutlet branch circuit.
Specific Sizing Guides & Calculators
Electric Range Circuit Breaker & Wire Size
What size breaker does an electric range need? Standard ranges require a 40 amp or 50 amp double-pole breaker on a dedicated 240V circuit per NEC requirements.
Electric Water Heater Breaker & Wire Size
What size breaker does a water heater need? Standard 4500W electric water heaters require a 30A double-pole breaker with 10 AWG copper wire per NEC rules.
Electric Dryer Breaker & Wire Size
Standard electric dryers require a 30 amp double-pole breaker with 10 AWG copper wire on a 240V circuit. Learn how to size your dryer circuit correctly per NEC.
3-Phase Circuit Breaker & Wire Size Calculator
Calculate 3-phase circuit breaker and wire size. Supports 208V, 240V, and 480V three-phase systems for motors, heaters, and continuous commercial loads.
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