Percent Error Calculator
Measure how far a measured value is from the true value, as a percentage.
Best for: Use it in chemistry and physics labs, calibration and QA, or any time you compare a measurement to a known reference value.
Purpose: Measure how far a measured value is from the true value, as a percentage.
Input
Result
ExactPercent error: 5% (measured is below the true value)
What to do next
Next: Significant Figures CalculatorMore about this result
- Type
- Exact Formula
- Method
- Standard mathematical formula
- Confidence
- High
A precise, deterministic calculation - the same inputs always give exactly this result.
A smaller percent error means a more accurate measurement. Whether a given error is acceptable depends on the field - a 5% lab error may be fine where a 0.1% engineering tolerance is not.
- Watch units and rounding — they change the answer.
- Order of operations matters; group terms carefully.
- Re-run with different inputs to sanity-check the result.
The same data can tell different stories - which average you use changes the answer.
How it's calculated & sources
Free & no sign-up · runs entirely in your browser. Results are estimates for general information, not professional advice — verify important decisions with a qualified expert. Last reviewed June 2026.
How it works
Percent error = |measured − true| ÷ |true| × 100. It measures how far a measured value is from the accepted (true) value; the sign is dropped.
Example
Measured 9.5 vs true 10 → |9.5 − 10| ÷ 10 × 100 = 5% error.
Frequently asked questions
Percent error vs percent difference?+
Percent error compares a measurement to a known accepted value (divide by the true value). Percent difference compares two measurements with no accepted 'true' (divide by their average).
Can percent error be negative?+
No — it uses absolute values, so it is always zero or positive. If you need direction, look at whether the measured value was higher or lower than the true value.
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