Efficiency calculator
Fill in what you know and leave the unknown box empty — it works out whichever one is missing. Nothing is uploaded; the arithmetic happens in your browser.
The formula
η = (useful ÷ total) × 100
Where this usually goes wrong
Efficiency can never exceed 100%. If it does, the two energies are in different units or the wrong way round.
Worked example
40 J useful from 100 J in is 40% efficient.
Those numbers are already in the boxes above — press Work it out to see it, then change them for your own.
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