Calculating your efficiency is straightforward once you know the Efficiency formula and what each input means. This guide explains the method in plain language, walks through a manual calculation, and gives worked examples you can follow — then you can do it instantly with the Efficiency Calculator.
What is Efficiency?
The Efficiency calculation tells you your efficiency from a few simple inputs. The figure you are solving for here is the efficiency, expressed in percent.
The Efficiency formula
The core formula is:
Efficiency = Useful output ÷ Total input × 100Here is what each input means:
- Useful output — a number. Example: 80.
- Total input — a number. Example: 100.
How to calculate it step by step
- Write down the useful output (for example, 80).
- Write down the total input (for example, 100).
- Apply the formula above to get your efficiency.
- Double-check the result with the Efficiency Calculator.
Worked examples
Example 1
| Input / Output | Value |
|---|---|
| Useful output | 80 |
| Total input | 100 |
| Efficiency | 80.00% |
| Energy lost | 20.00 |
With useful output of 80 and total input of 100, the efficiency works out to 80.00%.
Example 2
With useful output of 160 and total input of 100, the efficiency works out to 160.00%.
| Result | Value |
|---|---|
| Efficiency | 160.00% |
| Energy lost | -60.00 |
Example 3
With useful output of 40 and total input of 100, the efficiency works out to 40.00%.
| Result | Value |
|---|---|
| Efficiency | 40.00% |
| Energy lost | 60.00 |
Tips for an accurate result
- Keep your units consistent — mixing, say, months with years or grams with kilograms is the most common source of error.
- Round only at the very end. Rounding inputs early can shift the final answer noticeably.
- Re-run the numbers whenever an input changes, rather than estimating from an old result.
Prefer not to do the maths by hand? — the Efficiency Calculator does it instantly, for free, with the formula and a worked example built in.
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