Case 1
- Useful energy output
- 750
- Total energy input
- 1000
75.00%
Open with these valuesEfficiency Calculator
75.00%
Result: 75.00 %Efficiency is the useful output divided by the total input, times 100. Keep both figures in the same unit — joules and joules, watts and watts — so the units cancel and the answer is a clean percentage. Anything above 100 % means a typo or two different units, not a better machine.
Worked examples
Case 2
- Useful energy output
- 1200
- Total energy input
- 1500
80.00%
Open with these valuesCase 3
- Useful energy output
- 90
- Total energy input
- 100
90.00%
Open with these valuesHow it's calculated
efficiency = output ÷ input × 100
- StepPut the useful output and the total input in the same unit.
- StepDivide the output by the input.
- ResultMultiply by 100 to read the result as a percentage.
Reference table
| Output, input | Lost | Efficiency |
|---|---|---|
| 500, 1000 | half | 50 |
| 333, 1000 | two thirds | 33.3 |
| 750, 1000 | a quarter | 75 |
| 1200, 1500 | a fifth | 80 |
| 90, 100 | a tenth | 90 |
Questions
How do I calculate efficiency?
Divide the useful output by the total input and multiply by 100. For 750 J of useful output from 1000 J of input that is 75 %. Keep both in the same unit so they cancel.
What units does the efficiency calculator use?
Efficiency is a ratio, so the result is a plain percentage with no unit. Just make sure output and input are in the same unit — joules and joules, watts and watts, kWh and kWh.
Can efficiency be more than 100 %?
No. The useful output can never exceed the total input; that would create energy from nothing. A reading above 100 % means an input was mistyped or the two figures are in different units.
Why is no machine 100 % efficient?
Every real process loses energy to heat, friction, sound or light that does no useful work. A car engine turns about 20–35 % of its fuel into motion, an LED bulb reaches 80–90 %, a large electric motor can exceed 95 %.
Where is the output-over-input formula used?
Anywhere you compare what you get out against what you put in: rating engines, motors and pumps, grading appliances and power supplies, sizing solar panels and boilers. One percentage puts very different devices on one scale.
Sources and last check
Information, not professional advice.