How do you calculate horsepower from torque and RPM?

Power in watts equals torque in Newton-metres multiplied by angular velocity in rad/s. Angular velocity equals RPM times 2 pi divided by 60. So P (W) = torque times RPM times 2 pi divided by 60. Horsepower equals watts divided by 745.7. For example, 100 N-m at 2000 RPM gives 20944 W, which is 28.09 hp.

What is one horsepower in kilowatts?

One mechanical horsepower (hp) equals 745.7 watts or approximately 0.7457 kW. Metric horsepower (PS or CV) equals 735.5 watts (0.7355 kW). New Zealand and Australia typically rate engines in kilowatts, while the US uses hp and much of Europe uses PS.

What is the difference between mechanical and metric horsepower?

Mechanical horsepower (hp) equals 550 foot-pounds per second, which is 745.7 watts. Metric horsepower (PS) equals 75 kilogram-force metres per second, which is 735.5 watts. The difference is about 1.4 percent. This calculator uses mechanical horsepower for all conversions.

Horsepower Calculator

Horsepower is a unit of mechanical power deeply embedded in automotive, marine, and industrial engineering. One mechanical horsepower equals 745.7 watts, or roughly 550 foot-pounds of work per second. Despite the name, the unit is entirely independent of any actual horse. It persists in engine specifications, equipment ratings, and trade literature worldwide, sitting alongside kilowatts (used in New Zealand and Australia) and metric horsepower or PS (common in Europe and Japan). Converting between these three scales is a frequent task when comparing imported vehicles, matching motors to machinery, or reading datasheets from different countries. This calculator handles two jobs. The first is computing the mechanical power output of a rotating shaft from its torque and speed. You enter the torque in Newton-metres and the shaft speed in RPM, and the tool returns power in watts, kilowatts, mechanical horsepower, and metric PS. This is useful when a motor datasheet gives rated torque at a specific speed and you need the equivalent power in a different unit. The second mode converts directly between horsepower and kilowatts. Both modes update instantly as you type. Use the figures for specification and comparison work; your vehicle or motor documentation remains the authoritative source for rated output.

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Calculation mode

Torque

N·m

Speed

RPM

28.09 hp

mechanical horsepower

Power in watts20,944 W

Power in kW20.94 kW

Metric HP (PS)28.47 PS

How it works

For torque and RPM mode: power in watts = torque (N·m) times angular velocity (rad/s). Angular velocity = RPM times 2 pi divided by 60. So P = torque times RPM times 2 pi / 60. Mechanical horsepower = P divided by 745.7. Metric PS = P divided by 735.5. For the conversion mode: 1 hp = 0.7457 kW, so kW = hp times 0.7457, and these same watts, kW, and PS values are shown.

Worked example

A motor produces 100 N·m of torque at 2000 RPM. Angular velocity = 2000 times 2 pi divided by 60 = 209.44 rad/s. Power = 100 times 209.44 = 20,944 W = 20.94 kW. Mechanical horsepower = 20944 divided by 745.7 = 28.09 hp. Metric PS = 20944 divided by 735.5 = 28.47 PS. For the hp to kW mode: 1 hp = 0.7457 kW.

Related calculators

Torque to Horsepower: convert foot-pounds at RPM to horsepower in imperial units.
RPM Calculator: find the shaft speed of a wheel or motor in revolutions per minute.
Energy Converter: convert between joules, kilowatt-hours, BTU, and other energy units.
Force Calculator: calculate force, mass, or acceleration using Newton's second law.

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