Motor Amp Calculator

Estimate motor amps from horsepower, kilowatts, voltage, phase type, efficiency, power factor, and service factor. This calculator also estimates full-load amps, adjusted amps, starting amps, kVA, watts, breaker planning size, and fuse planning size.

Calculate Motor Amps

Motor amps = output watts ÷ (volts × efficiency × power factor). Three-phase uses √3 × volts.
Your result will appear here.

How the motor amp calculator works

Motor power:
The calculator converts horsepower to watts, or uses entered kW, watts, or nameplate amps.

Motor current:
It estimates current using voltage, phase type, efficiency, and power factor.

Planning values:
It estimates adjusted amps, starting amps, breaker planning size, fuse planning size, kVA, and comparison motor amps.

Why use a motor amp calculator?

A motor amp calculator helps estimate the current a motor may draw so you can plan circuits, panels, breakers, fuses, wire size, and equipment loads.

It can help with pumps, fans, compressors, shop tools, conveyors, HVAC equipment, and general motor load planning.

What your result means

Your result shows full-load amps, adjusted amps, starting amps, motor watts, input watts, kW, kVA, horsepower, voltage, efficiency, power factor, service factor, breaker planning size, and fuse planning size.

Motor amp calculator formulas

Frequently asked questions

How do I calculate motor amps?

Convert horsepower to watts, then divide by voltage, efficiency, and power factor. For three-phase motors, also divide by √3.

Why are motor starting amps higher than running amps?

Motors often draw high inrush current when starting because the rotor is not yet moving and back EMF is low.

Should I use calculated amps or nameplate amps?

For real installations, use the motor nameplate and applicable electrical code. Calculated amps are useful for early planning only.

Can this size the final breaker and wire?

No. This calculator gives planning estimates. Final motor conductor, breaker, fuse, overload, disconnect, and starter sizing must follow code and manufacturer instructions.