Horsepower Calculator

This calculator converts power between kilowatts and horsepower, and works out engine power from torque and engine speed, the two questions people most often have about how much an engine can do. Power is the rate of doing work, and it comes in two common units: the kilowatt, the SI unit used on New Zealand vehicle specifications and electricity, and horsepower, the older unit coined to compare engines with draught horses and still quoted everywhere in the motoring world. Being able to move between them is genuinely useful when comparing cars, motors and machinery. This tool does both jobs. Enter a power figure in kilowatts and it gives the equivalent in mechanical horsepower, using the standard factor where one horsepower is about 0.7457 kilowatts. Separately, enter an engine's torque in newton metres and its speed in revolutions per minute, and it calculates the power being produced, since power is torque times rotational speed. This reveals the relationship at the heart of engine performance: the same power can come from high torque at low revs or lower torque at high revs, which is why peak power and peak torque occur at different engine speeds. The calculator shows the power from torque and revs in both kilowatts and horsepower. Everything updates as you type, so you can compare figures quickly. Use it to compare vehicle outputs, to convert a quoted power figure, or to understand how torque and engine speed combine to make power. The calculations use the standard conversion constants and are rounded for display.

One mechanical horsepower = 0.7457 kW. Power (kW) from torque = torque x RPM / 9549. Rounded for display.