Horsepower to Amps Calculator

Enter horsepower, voltage, power factor, and phase to calculate the current a motor draws from the electrical supply.

How to Use the Horsepower to Amps Calculator

Horsepower, voltage, and power factor go in; the phase toggle decides whether the current comes out divided by one line or spread across three. Everything updates as you type.

This is the direction that actually matters when wiring a motor: the nameplate already says how many horsepower it's rated for, and what's needed is the current a breaker, contactor, or cable has to be sized for.

Single-phase: I = (HP × 745.7) ÷ (V × PF)
Three-phase:  I = (HP × 745.7) ÷ (√3 × V × PF)

A 5 HP single-phase motor at 230V with a 0.8 power factor draws about 20.3A. Move a 10 HP motor to a 460V three-phase supply — a standard industrial voltage — with a slightly better 0.87 power factor, and current comes out to roughly 10.76A per line, despite the horsepower doubling. Higher voltage and three-phase distribution both push current down for a given power output, which is exactly why larger industrial motors run at higher voltages rather than staying on 230V.

The 745.7 W/HP figure is mechanical (imperial) horsepower specifically. A motor spec sheet quoting metric horsepower (PS) instead — common on European equipment — is describing a slightly smaller unit (735.5 W), and feeding a PS rating into this formula unmodified will overstate the current by about 1.4%. Confirm which "horsepower" a nameplate actually means before wiring against this result.

Power factor still matters as much here as it does for a straightforward kW-to-amps conversion — assume 1.0 for convenience and the calculated current comes out low, which is precisely the kind of undersizing mistake that shows up later as a breaker that trips under real load.