How do you calculate power?

Power is the ratio of work done on a system in relation to the time it took to do the work, so calculating power is a matter of dividing work by time. Calculating power can be handy for finding out how efficient or strong a car engine is.

1. Determine how much force was exerted.

   Force is the fundamental component of motion, and it is measured in newtons. Assume, for example, that you're dealing with a 50-kilogram person under normal Earth gravity. Determining the force is a matter of multiplying the mass by the gravitational pull of Earth, yielding a result of 490 newtons. For basic power calculations, forces such as friction are often disregarded.

2. Multiply the force by the distance

   Because the person weighs 490 newtons, multiplying it by 5 yields 2,450. The unit for work is the joule. Therefore, the person does 2,450 joules of work by moving 5 meters.

3. Divide this result by the time it took

   Depending on whether the person walked, power-walked or sprinted, this yields different results. At a leisurely walking pace, assume it took about 10 seconds to cover 5 meters, and express the result in watts. The person had 245 watts of power. A power walk done in 5 seconds yields 490 watts, and someone sprinting the distance in 3 seconds yields 816.67 watts.