Fuse Sizing Calculator Formula

Understand the math behind the fuse sizing calculator. Each variable explained with a worked example.

Use the Fuse Sizing Calculator

Formulas Used

Minimum Fuse Rating

min_fuse = operating_current * safety_factor

Variables

VariableDescriptionDefault
operating_currentOperating Current(A)5
safety_factorSafety Factor1.25

How It Works

Fuse Sizing

Fuse >= I_operating x Safety_Factor

Standard practice: 1.25 (125%) for continuous loads. Round up to next standard fuse value.

Worked Example

Circuit draws 5 A normally.

operating_current = 5safety_factor = 1.25
  1. 01Min fuse = 5 x 1.25 = 6.25 A
  2. 02Use a 7 A or 7.5 A standard fuse.

Ready to run the numbers?

Open Fuse Sizing Calculator