Power Calculator

Watts, kilowatts and horsepower, with a running cost.

Watts, kilowatts and horsepower, with a running cost. Power is energy divided by time — a rate, not an amount.

Written and maintained by Mohit PatelLast checked August 4, 2026How we build these

Energy

Time

Electricity rate

per kWh

Optional — for the running cost.

Power (watts)

1,000

1 kW · 1.341 hp

Power1,000 W

In kilowatts1

In horsepower1.341

Energy per hour1 kWh

Power is energy divided by time — the rate of doing work, not an amount of it. One horsepower is 745.7 W, defined from 550 foot-pounds per second, which James Watt estimated as what a dray horse could sustain. A kilowatt-hour, the unit on an electricity bill, is 3.6 million joules.

How the Power Calculator works

Power is energy divided by time — a rate, not an amount. One horsepower is 745.7 watts, defined from 550 foot-pounds per second, which James Watt estimated as what a dray horse could sustain. A kilowatt-hour is 3.6 million joules.

Also known as: watts calculator · horsepower calculator · power formula physics · how to calculate power

Where to go next

The Power question rarely arrives on its own. These are the ones that usually come with it:

Work Calculator — W = Fd cos θ, including the case that comes out zero.
Kinetic Energy Calculator — ½mv², and why doubling speed quadruples the damage.
Power Factor Calculator — Real against apparent power, and the current it costs.
Speed Distance Time Calculator — Any one of the three from the other two, in four units.

Sources

Frequently asked questions

How do I calculate power?

Divide energy by time. 3.6 million joules over an hour is 1,000 watts, or 1 kW.

How many watts is one horsepower?

745.7 for mechanical horsepower. Metric horsepower is slightly different at 735.5, which is a common source of small discrepancies in specifications.

What is a kilowatt-hour?

The energy used by a 1 kW device running for an hour — 3.6 million joules. It is the unit an electricity meter counts, which is why this page can convert power into a running cost.

What is the difference between power and energy?

Energy is the quantity; power is the rate. A bill charges for kilowatt-hours of energy, while the appliance is rated in watts of power.

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The one-line version

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