Horsepower to Amps Calculator
Estimate the full-load current of an electric motor from its horsepower rating, efficiency and power factor.
How to use the Horsepower to Amps Calculator
- Choose the motor type.
- Enter the motor output and pick its unit.
- Enter the voltage.
- Enter the efficiency.
- Enter the power factor.
- Press Calculate. The result updates automatically as you type, and you can switch the result unit at any time.
About the Horsepower to Amps Calculator
A motor's horsepower rating is mechanical output at the shaft. To get there it must draw extra electrical power to cover losses in its windings, bearings and fan, and on AC it also draws reactive current that raises the amps without adding watts. This calculator combines those effects to estimate running current at full load.
Typical values: small single-phase motors are 60–80% efficient with power factors of 0.7–0.85; premium three-phase motors above 10 hp reach 90–95% efficiency and 0.85–0.9 PF. Starting (inrush) current is often five to seven times the running current, which is why motor circuits use special breaker and overload sizing rules.
Formula
Input power = hp × 745.7 ÷ η
DC: I = Input ÷ V
Single-phase: I = Input ÷ (V × PF)
Three-phase: I = Input ÷ (√3 × V × PF)
η is efficiency as a decimal. Horsepower ratings describe shaft output, so the motor draws more electrical power than its rating because of internal losses.
Example calculation
Using the default values:
- Motor type = AC single-phase
- Motor output = 2 hp
- Voltage = 230 V
- Efficiency = 80%
- Power factor = 0.85
the calculator returns:
- Estimated current: 9.54 A
- Electrical input power: 1,864.2 W
Frequently asked questions
How many amps does a 1 hp motor draw?
Roughly 13–16 A at 115 V single-phase, or about 7–8 A at 230 V. A three-phase 1 hp motor at 460 V draws around 2 A.
Why is the result different from the nameplate?
Nameplate full-load amps come from testing the actual motor. Efficiency and power factor vary by design and load, so always prefer the nameplate figure when you have it.
How many watts is one horsepower?
One mechanical horsepower equals about 745.7 W of output.
Last updated: · Category: Electrical calculators