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Fuse Size Calculator

Find the correct fuse size using the NEC 125% continuous-load rule.

Introduction

Fuse Size Calculator — Find the correct fuse size using the NEC 125% continuous-load rule. Enter Continuous load (A) to get an instant, accurate result.

Formula

Same NEC 210.20(A) 125% continuous-load rule used for breakers applies to fuse selection: required rating = continuous load × 1.25, rounded up to the next standard NEC 240.6(A) size.

Step-by-step

  1. Enter the Continuous load (A).
  2. Click Calculate to see your result instantly.

Real-world example

Example: With Continuous load (A) = 16, the Fuse Size Calculator gives Fuse Amps: 20, Required Min Amps: 20.

Frequently Asked Questions

Are fuses sized differently than breakers?
No — the NEC treats fuses and circuit breakers the same way for overcurrent protection sizing purposes; both use the same 125%-of-continuous-load rule and the same standard ampere ratings in 240.6(A).
Can I round down instead of up to a standard size?
No — the required minimum rating (load × 1.25) must be met or exceeded, so you always round up to the next standard size at or above that value.
What inputs does the Fuse Size Calculator need?
You'll need to provide: Continuous load (A). All fields use sensible defaults, so you can see a working example immediately and then adjust the values to match your own numbers.
How accurate is the Fuse Size Calculator?
The Fuse Size Calculator applies the formula exactly as calculated — Same NEC 210.20(A) 125% continuous-load rule used for breakers applies to fuse selection: required rating = continuous load × 1.25, rounded up to the next standard NEC 240.6(A) size. — so results are precise for the inputs you provide. Accuracy depends on entering correct, realistic input values.
Is the Fuse Size Calculator free to use?
Yes, the Fuse Size Calculator is completely free, requires no signup, and runs instantly in your browser.

About the Fuse Size Calculator

The Fuse Size Calculator uses a real, verifiable formula — Same NEC 210.20(A) 125% continuous-load rule used for breakers applies to fuse selection: required rating = continuous load × 1.25, rounded up to the next standard NEC 240.6(A) size. — so results are accurate every time, not an approximation.