HP to Amps Calculator
How many amps a motor of a given horsepower draws, with efficiency and power factor included.
The formula
A = hp × 746 / (V × efficiency × PF)
(times √3 in the denominator for three-phase). One horsepower is 746 W of mechanical output; the motor draws more electrical power than that because nothing is 100% efficient. A 1 hp motor at 230 V, 85% efficiency and PF 0.85 draws about 5.3 A.
Nameplate beats calculation
This gives a realistic estimate for sizing cable and breakers, but the motor's own nameplate full-load amps (FLA) is the authoritative number, and code sizing rules work from it. Remember starting current: an induction motor started direct-on-line pulls 5 to 7 times FLA until it spins up, so protective devices are chosen to ride that through rather than trip instantly.