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Power Calculator

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Enter any two of work, time, and power - the third is calculated automatically.

Power Calculator

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Power =
50 W
For converting a power value between watts, horsepower, and other units, see our Power Converter.

The formula

Power = Work / Time
Example

500 joules of work done in 10 seconds: power = 500/10 = 50 watts.

Step-by-step guide

  1. Fill in any two values - work, time, or power - and leave the third blank.
  2. Read the calculated result.

Why power is about speed, not just total effort

Two people can do the exact same amount of work - say, carrying identical boxes up the same flight of stairs - but the one who does it faster has a higher power output, even though the total energy expended is identical. Power specifically measures the rate at which work is done, which is why a more powerful engine isn't necessarily one that can eventually move more total weight, but one that can do a given amount of work more quickly.

Common mistakes

Confusing power with total energy or work - a low-power device can still eventually deliver a large amount of total work, it just takes longer to do so.
Mixing up watts (power) with watt-hours or kilowatt-hours (energy) - these describe different physical quantities, related by time.

Frequently asked questions

What unit is power measured in?

Watts (W) in the SI system - one watt equals one joule of work done per second. Power is also commonly expressed in horsepower, especially for engines and motors.

How do I convert this result to horsepower or other power units?

Use our Power Converter to convert a watts result into horsepower, kilowatts, or BTU per hour.

How is this different from electrical power (P = VI)?

Both describe the same underlying concept - a rate of energy transfer - just calculated differently depending on context. Mechanical power here comes from work over time; electrical power comes from voltage and current, calculable with our Ohm's Law Calculator.

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