Horsepower Calculator
Find horsepower from torque and RPM, from an electric motor’s volts and amps, or from a load and speed.
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Horsepower
- Kilowatts
- Watts
- Metric hp
- BTU per hour
- Also
- Standard Motor
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| Name | From | HP | kW | Remove |
|---|
How to Calculate Horsepower
One mechanical horsepower is 33,000 foot-pounds of work per minute, or 745.7 watts. Every horsepower formula is a way of getting to that.
From torque: hp = torque (lb-ft) × RPM ÷ 5,252
From force and speed: hp = force (lb) × speed (ft/min) ÷ 33,000
Electric motor output: hp = V × A × efficiency ÷ 746 (DC) × PF (single-phase) × PF × 1.732 (three-phase)
Torque and horsepower are equal at 5,252 RPM, which is why engine dyno charts in lb-ft and hp always cross there.
Worked Example
Power Units
| Unit | In Watts | In hp |
|---|---|---|
| Mechanical horsepower (hp) | 745.7 | 1 |
| Metric horsepower (PS, CV) | 735.5 | 0.9863 |
| Kilowatt | 1,000 | 1.341 |
| BTU per hour | 0.2931 | 0.000393 |
Tips
Motor nameplates list output (shaft) horsepower, not input. Engine horsepower at the crank is higher than at the wheels because of drivetrain losses. For quarter-mile estimates, see the horsepower from quarter mile calculator.