Efficiency Calculator
Efficiency is the ratio of what you get out to what you put in, and it is the number that decides whether a machine is worth running at all.
Efficiency
75.00%
- Energy lost
- 25.00%
- Wasted input
- 250
- Output to loss ratio
- 3
Values update as you type. This calculator covers the single scenario its formula assumes — see Common Mistakes for what it leaves out.
The formula this calculator uses
efficiency = useful output / total input
- eta
- Efficiency, usually as a percentage
- Eout
- Useful output energy or power
- Ein
- Total input energy or power
How to check the result by hand
- 1
Measure the total input
This is everything you supplied: electrical power drawn, fuel energy burned, or work put in by hand. It is always the larger of the two numbers, and it is the denominator.
- 2
Measure the useful output
Count only the output that does the job. Waste heat leaving through a radiator is not useful output for a motor, even though it is real energy.
- 3
Put both in the same unit
Watts with watts, or joules with joules. If you measured one as power and the other as energy over a known time, convert first so the ratio is dimensionless.
- 4
Divide output by input
Seven hundred and fifty divided by a thousand is 0.75. This decimal is the efficiency, and it will always be a number between zero and one for a real device.
- 5
Turn it into a percentage if needed
Multiply the decimal by a hundred to get seventy five percent. Keep the decimal form when it feeds into a further multiplication, such as a chain calculation.
For worked examples, common mistakes and the limits of this formula, read the full How To Calculate Efficiency page.