Horsepower Calculator — convert watts to horsepower

How it works

Horsepower (hp) and the watt (W) both measure power — the rate of doing work — they are just different units. One horsepower is 746 watts (the value used by OpenStax), so converting is a single division:

hp = watts ÷ 746

To go from kilowatts (kW), multiply by 1000 first, or divide the kilowatts by 0.746. The unit dates to James Watt, who compared his steam engines to the pulling power of draught horses; today it is still used for car and motorcycle engines, while the watt is the SI unit used in physics and for electric motors.

There are a few slightly different "horsepower" definitions: mechanical (imperial) horsepower is 745.7 W, electrical horsepower is exactly 746 W, and metric horsepower (PS) is about 735.5 W. This calculator uses 746 W, OpenStax's rounded value — practically identical to mechanical horsepower and exactly the electrical one.

Worked example

By definition, 746 watts is exactly 1 hp. A small 250 W e-bike motor is about 0.34 hp. A 100 kW (100,000 W) electric car motor is 100000 ÷ 746 ≈ 134 hp, and a 150 kW motor is about 201 hp. Double the wattage and you double the horsepower.

Frequently asked questions

How do I convert watts to horsepower?

Divide the power in watts by 746, since one horsepower equals 746 watts. For kilowatts, multiply by 1000 first (or divide the kW figure by 0.746). For example 50,000 W ÷ 746 ≈ 67 hp.

How many watts are in one horsepower?

One horsepower is 746 watts. So 1 hp = 746 W, 10 hp = 7460 W, and 100 hp ≈ 74,600 W (about 74.6 kW). This is the conversion used for engine power ratings.

What is the difference between mechanical and metric horsepower?

Mechanical (or imperial) horsepower is about 745.7 W, and the closely related electrical horsepower is exactly 746 W — the value this calculator uses. Metric horsepower (PS, or "cheval") is about 735.5 W and is common in continental Europe, so a car rated in PS shows a slightly higher number than the same engine in hp.

How is horsepower related to torque and RPM?

For a rotating engine, horsepower can be found from torque and speed: hp = (torque in lb-ft × RPM) ÷ 5252. That formula and this watt conversion measure the same power — you would get the same horsepower after converting the torque-and-RPM result from ft-lb per minute into watts.

Why is horsepower still used for cars?

Tradition and familiarity. Engine power has been quoted in horsepower since the early days of the automobile, so buyers and enthusiasts think in those terms. Physicists and electric-motor makers use watts and kilowatts, which is why EV power is often given in kW — divide by 0.746 to compare it in horsepower.

How much horsepower does a person produce?

A fit person sustains well under 1 hp — around 0.1 hp (about 75 W) for long periods, though a trained athlete can briefly exceed 1 hp in a sprint. That is why it takes an engine of many horsepower to do work a person cannot.