Fuse Size Calculator

How to Select the Correct Fuse Size

A fuse is a sacrificial overcurrent protection device. When too much current flows, the fuse element melts and breaks the circuit before damage occurs. Selecting the right fuse size is critical: too small and it blows under normal operation; too large and it won't protect the circuit.

Fuse Sizing Rule

Fuse Rating = Load Current × 1.25 (safety factor)

Then select the nearest standard fuse rating above this value. Standard fuse ratings: 1A, 2A, 3A, 5A, 6A, 10A, 13A, 15A, 20A, 25A, 30A, 40A, 50A, 60A, 80A, 100A.

For motor loads (high starting current): Fuse Rating = Motor Full-Load Amps × 1.5 to 2.5 (time-delay fuse).

How to Use This Calculator

Enter the load power (watts) and supply voltage, or enter current directly. Select load type (resistive, inductive/motor). The calculator recommends the correct fuse rating.

Practical Examples

Example 1: 1,200W kettle on 230V. I = 1,200 / 230 = 5.22A × 1.25 = 6.5A → use 7A or 10A fuse.

Example 2: 1HP (746W) single-phase motor at 230V, FLA = 4A. Time-delay fuse = 4 × 2.0 = 8A → use 10A time-delay fuse.

Example 3: UK plug fuse for a 100W lamp. I = 100/230 = 0.43A × 1.25 = 0.54A → use 1A or 3A fuse (standard UK sizes).