Fuse Size Calculator

Fuses are the quiet guardians of the panel: no lever, no label reader, just a calibrated element that parts company with the circuit the moment it is asked for too much.

Fuse Size Calculator suggests a standard fuse rating from the circuit current, the continuous portion and the load type - picking gG or aM guidance and showing the minimum conductor ampacity alongside.

It is a planning aid. Final selection must follow the code and the fuse manufacturer data in force.

• Load in amps: Enter the measured or computed current.
• Continuous load: 125% applied to continuous parts.
• gG or aM: Load-type guidance for the fuse class.
• Standard ratings: Next IEC/NEC fuse size chosen for you.
• Conductor check: Minimum ampacity for the cable.
• Single or 3-phase: Formula aware of the system.
• Export: Copy or download as text, CSV or JSON.

1. Enter the load current in amps.
2. Enter the continuous portion of that load.
3. Choose the load type (general, motor, transformer).
4. Select the standard in force.
5. Read the suggested fuse size and minimum cable ampacity.
6. Export the sizing note if needed.

Example 1 — Heater circuit. 23 A continuous at 230 V: design 28.75 A, an 32 A gG fuse, cable at least 29 A.

Example 2 — Motor. 20.8 A FLA: an aM fuse close to 25 A, or a gG at 32 A to ride the start.

Example 3 — Mixed. 10 A continuous plus 6 A non-continuous: 18.5 A design, a 20 A fuse.

Example 4 — 3-phase. 24.1 A running at 400 V: 25 A aM or 32 A gG with a matching cable.

• Design current right: Continuous 125% applied automatically.
• Rating picked: Next standard fuse size chosen.
• Class guidance: gG versus aM matched to the load.
• Wire matched: Minimum conductor ampacity shown.
• Free and private: No uploads, no accounts, no logging.