How to use this calculator
- Enter or choose measured (experimental) value.
- Enter or choose true (accepted) value.
- The percent error updates as you type. Use Copy result or Share to keep it.
Method
Percent error = |Measured − True| ÷ |True| × 100
- Measured
- the value you obtained
- True
- the accepted or reference value
Worked example
- Absolute error = |52 − 50| = 2.
- Percent error = 2 ÷ 50 × 100 = 4%.
Measuring 52 when the true value is 50 is a 4% error, on the high side.
What the result means
A small percent error means the result is accurate, not that it is precise: repeated measurements can all be close to each other and still share the same bias.
Assumptions and limits
- The true value is known and is not 0.
- When the true value is 0 or very close to it, percent error is undefined or explodes; report the absolute error instead.
Questions
Can percent error be negative?
The usual definition uses the absolute value, so it is never negative. Some lab courses keep the sign to show whether the result was high or low; the calculator shows both.
Is percent error the same as percentage change?
The arithmetic is similar, but percent error compares against a true value, while percentage change compares a new value against an old one.