Enter your motor's horsepower (HP), voltage (V), efficiency (%), and power factor to calculate the electric current in amps. Choose between DC, single-phase AC, or three-phase AC circuits — the calculator applies the correct formula automatically and returns the full-load amps your motor draws.
Current (Amps)
--
Power Output
--
Input Power (accounting for efficiency)
--
Formula Used
--
Horsepower (HP) measures mechanical output power, while amps measure electric current flowing into a motor. Converting HP to amps estimates the full-load input current a motor draws from its power supply given its output power rating. This is essential for sizing wiring, fuses, and circuit breakers correctly.
The formula depends on the circuit type. For DC: I = (HP × 746) / (V × η). For single-phase AC: I = (HP × 746) / (V × PF × η). For three-phase AC: I = (HP × 746) / (√3 × V × PF × η). Here, V is voltage, η is efficiency (as a decimal), and PF is power factor.
Horsepower is a unit of power — it describes how much work a motor can do. Amps is a unit of electric current — it describes how much electricity flows through the circuit to produce that power. They are related through voltage, efficiency, and power factor.
Assuming single-phase AC, 90% efficiency, and a 0.9 power factor, a 1 HP motor at 120V draws approximately: I = (1 × 746) / (120 × 0.9 × 0.9) ≈ 7.67 amps. Actual values vary depending on your motor's rated efficiency and power factor.
For a DC motor at 12V and 90% efficiency, the current is: I = (1 × 746) / (12 × 0.9) ≈ 69.07 amps. DC motors at low voltages draw very high current, which is why higher voltages are preferred for powerful motors.
Motors are not 100% efficient — some input power is lost as heat. Efficiency accounts for this loss so the calculated current reflects real-world input, not ideal output. Power factor (for AC circuits) accounts for the phase difference between voltage and current, which increases the actual current drawn from the supply.
Most AC induction motors have a power factor between 0.80 and 0.95 at full load. At partial loads, the power factor is lower. If you don't know your motor's power factor, 0.85–0.90 is a reasonable estimate for general calculations.
Yes — the HP to amps conversion formulas apply to any electrical device rated in horsepower, including generators, pumps, compressors, and fans. Just make sure you use the correct voltage, efficiency, and power factor for your specific device.