Energy Efficiency Calculator
Enter any two of output energy, input energy and efficiency to find the missing value plus the energy lost as heat. Works for engines, motors and machines.
How to use the efficiency calculator
- Enter any two of output energy, input energy and efficiency percentage.
- Leave the value you want to find blank.
- Read the missing value and the energy lost (input minus output).
Examples
Output and input energy
output = 80 J, input = 100 J
efficiency = 80%, lost = 20 J
Output and efficiency
output = 80 J, efficiency = 80%
input = 100 J, lost = 20 J
Frequently asked questions
What is the efficiency formula?
Efficiency is the useful output divided by the total input, expressed as a percentage: efficiency = output / input x 100.
How is energy lost calculated?
Lost energy is input minus output. In a real machine this energy usually leaves as heat, sound or friction rather than useful work.
Can efficiency be more than 100%?
No. Useful output cannot exceed the energy put in, so efficiency stays at or below 100%. The calculator rejects an output larger than the input.
What units should I use?
Any consistent energy or work unit works, such as joules, kilojoules or watt-hours, as long as output and input use the same unit.
Does it work for power as well as energy?
Yes. Because efficiency is a ratio, you can enter output and input as power in watts instead of energy in joules and get the same percentage.
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