Power Calculator (P = W / t)

This power calculator uses P equals work divided by time, the rate at which work is done or energy is transferred. Choose the unknown and enter the others; the calculator solves for power, work (or energy) or time. Power tells you how quickly energy is used: doing the same work in less time needs more power. It is measured in watts, where one watt is one joule per second. The same formula covers mechanical power, electrical energy use and more. The formula, a worked example and the assumptions are below.

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Power (W)

Work / energy (J)

Time (s)

Solve for

Value

Result

The formula

Power is P = W / t, work or energy divided by the time taken. Rearranged: W = Pt and t = W / P. One watt is one joule per second.

Worked example

Doing 100 joules of work in 20 seconds is a power of P = 100 / 20 = 5 watts. Solve for P with W = 100, t = 20 to confirm.

Frequently asked questions

What is power?

The rate of doing work or transferring energy, work divided by time, measured in watts.

What is a watt?

One joule per second. A 60 watt bulb uses 60 joules of energy every second.

How is power related to work?

Power is work per unit time, so work equals power times time.

Who this calculator is for

This calculator is for physics students, teachers and engineers.

What this calculator assumes

You enter SI units as labelled.
One variable is solved from the others.
Results are rounded for display.

Formula and sources

Related calculators

Kinetic Energy Calculator: energy of motion.
Momentum Calculator: mass times velocity.
Projectile Motion Calculator: range and height.

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