How this calculator works
Percent error = |measured − accepted| ÷ |accepted| × 100.
The absolute value means percent error is always positive; the signed error shows whether the measurement was over or under.
Absolute error is the plain difference in the original units.
The accepted value can’t be zero, because the error would be undefined.
Report percent error to a sensible number of digits, usually two or three significant figures, matching the precision of your measurements.
Worked example
Measuring gravity as 9.6 m/s² (accepted 9.81)
- Difference: |9.6 − 9.81| = 0.21.
- Percent error: 0.21 ÷ 9.81 × 100 = 2.14%.
- Signed: −2.14%, below the accepted value.
Questions people ask
What is a good percent error?
It depends on the experiment. In many school labs under 5% is considered good; precision measurements need far less.
Is percent error the same as percent difference?
No. Percent error compares with a known true value; percent difference compares two measurements using their average.
Can percent error be over 100%?
Yes, if the measurement is more than double the accepted value or wildly off.
How do I reduce percent error?
Repeat measurements and average them, calibrate instruments and reduce sources of systematic error.
What is the difference between accuracy and precision?
Accuracy is how close a result is to the true value, which percent error measures. Precision is how close repeated measurements are to each other, measured by their spread.
Last reviewed October 2, 2026