Energy Efficiency Calculator

Efficiency is the useful output divided by the total input, expressed as a percentage: efficiency = output / input x 100. An output of 80 J from an input of 100 J is 80 percent efficient. The remaining 20 percent is the fraction that did not become useful work.

Energy lost is simply input minus output. In a real machine this portion leaves as waste heat, sound, vibration or friction rather than useful work. The lost figure and the efficiency percentage describe the same shortfall from two angles.

No. Useful output cannot exceed the energy put in, so efficiency stays at or below 100 percent. If you enter an output larger than the input, or an efficiency above 100, the calculator returns an error instead of a result.

Only the energy that does the job you care about, such as motion from a motor or light from a bulb. Everything else the device produces, mostly heat, is a loss. Defining useful output narrowly gives a lower, more honest efficiency than counting waste heat as a product.

Any consistent energy or work unit works, such as joules, kilojoules, calories or watt-hours, as long as output and input share the same unit. The calculator does not convert units, so keep both figures in one unit and the efficiency percentage will be correct.

Yes. Because efficiency is a ratio, you can enter output and input as power in watts rather than energy in joules and get the same percentage. The Energy lost card is then really power lost, in the same units you entered.

Exactly two of the three: output plus input, output plus efficiency, or input plus efficiency. The 'Known values' menu sets which pair you enter, and the tool computes the remaining quantity plus the energy lost from it.

This calculator reports the straightforward output-over-input ratio. Real machines lose energy to friction, electrical resistance, air drag and heat, and heat engines face a hard ceiling set by thermodynamics, so measured efficiency is often well below a naive expectation.