Horsepower Calculator
Use this horsepower calculator to convert between horsepower, kilowatts, watts, ft·lbf/s and BTU/h, to find horsepower from torque and RPM, and to estimate electric motor horsepower from volts, amps, power factor and efficiency. It covers mechanical horsepower (745.7 W), metric horsepower or PS (735.5 W) and electrical horsepower (746 W). This page is for horsepower, kW and torque conversion. To turn a power rating into amps use the amp calculator, for torque on its own see the torque calculator, and for volts, amps and watts see the Ohm's law calculator.
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Convert power units
Horsepower (mechanical, 745.7 W)
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Metric horsepower (PS, 735.5 W)
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Electrical horsepower (746 W)
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kW
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W
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ft·lbf/s
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BTU/h
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Horsepower from torque and RPM
Horsepower (mechanical, 745.7 W)
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kW
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Metric horsepower (PS, 735.5 W)
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W
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Electric motor horsepower from volts and amps
Shaft output (HP)
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Shaft output (kW)
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Electrical input (kW)
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Mechanical horsepower is 745.7 W, which is 550 ft·lbf/s. HP = torque (lb·ft) × RPM ÷ 5252, and in metric kW = torque (N·m) × RPM ÷ 9549.3. This page uses the exact 2π conversion, so it can differ slightly from the rounded constants. Motor shaft HP = volts × amps × efficiency × power factor (× √3 for three-phase) ÷ 745.7. Power factor does not apply to DC. The motor values (230 V, 10 A, 0.85 power factor, 85% efficiency) are placeholders to edit, so use your motor's nameplate.
More in this group
- Torque Calculator Torque from force, arm, power and RPM, with unit conversion.
- Amp Calculator Watts, kW, kVA or HP to amps, and amps back to power.
- Ohms Law Calculator Find volts, amps, ohms and watts from any two values.
- Voltage Drop Calculator Volts lost, percent drop and minimum wire size for a cable run.
How it works
- How many watts are in a horsepower?
- One mechanical horsepower is 745.7 W, or 0.7457 kW, which equals 550 ft·lbf/s or about 2,544 BTU/h. Going the other way, 1 kW is about 1.341 HP. Metric horsepower (PS) is 735.5 W and electrical horsepower is 746 W.
- How do I calculate horsepower from torque and RPM?
- Horsepower = torque in lb·ft × RPM ÷ 5252. For 200 lb·ft at 3,000 RPM that is 200 × 3,000 ÷ 5252 = 114.2 HP. In metric, kW = torque in N·m × RPM ÷ 9549.3. To go the other way, from power to torque, see the torque calculator.
- How do I find motor horsepower from volts and amps?
- Multiply volts by amps, then by power factor for AC and by √3 for three-phase, to get input watts. Multiply by efficiency and divide by 745.7 to get shaft horsepower. A single-phase 230 V, 10 A motor at 0.85 power factor and 85% efficiency delivers about 2.2 HP. Use your motor nameplate for real values.
- What is the difference between HP, PS and electrical horsepower?
- They are slightly different units. Mechanical HP is 745.7 W, metric horsepower (PS, also called CV) is 735.5 W and electrical horsepower is 746 W. So 1 HP is about 1.014 PS. Check which one a spec sheet uses.
- How is this different from the amp calculator?
- This page converts horsepower, kW and torque, and estimates motor HP from measured volts and amps. The amp calculator goes from a power rating (W, kW, kVA or HP) to the current in amps at a given voltage, which is what you need for sizing circuits.