Percent error calculator
Calculator
The calculator needs JavaScript. The tables below give the same numbers for common cases.
How it is worked out
- Error = |observed − true| = |9.6 − 9.81| = 0.21.
- Divide by the true value and multiply by 100: 0.21 ÷ 9.81 × 100 = 2.1407%.
| Inputs | Answer |
|---|---|
| Observed (measured) value: 9.6; True (accepted) value: 9.81 | The percent error of 9.6 against 9.81 is 2.1407%. |
| Observed (measured) value: 102; True (accepted) value: 100 | The percent error of 102 against 100 is 2%. |
| Observed (measured) value: 47.5; True (accepted) value: 50 | The percent error of 47.5 against 50 is 5%. |
How to use it
Percent error = |observed − true| ÷ |true| × 100. It tells you how large a measurement error is relative to the true value. A measurement of 9.6 against an accepted 9.81 has a percent error of about 2.14%.
The calculator also shows the absolute error and the signed error (negative means the measurement was below the true value).
Frequently asked questions
How do I calculate percent error?
Take the absolute difference between measured and true values, divide by the true value and multiply by 100.
Can percent error be negative?
The usual formula uses the absolute value, so it is not; the signed version shows the direction.
What if the true value is 0?
Percent error is not defined, because you would divide by 0.
Method: standard arithmetic shown step by step; no outside data is used. Checked 2026-11-12.
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General information only. Results are plain arithmetic on the numbers you enter; check anything important (money, health, school work) against your own records or the official source.