Math

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Percent Error Calculator.

Calculate absolute and signed percent error from measured and accepted values.

On-device calculationNo signup
01

Set your values

Results update as you type.

percentError: 3 %

percentError

0.000000%
signedPercentError: -3 %

signedPercentError

0.000000%

Results update automatically as you type.

Use Cases

Science Lab Experiments

Check how accurate your experimental measurements are compared to theoretical or known values.

Example: If you measure 9.8 m/s² for gravity and the accepted value is 9.81 m/s², the percent error is about 0.1%.

Quality Control in Manufacturing

Evaluate how closely a produced part's measurement matches the specified target.

Example: A part measures 10.2 mm but the spec is 10.0 mm, giving a 2% error.

Frequently Asked Questions

What is percent error?
Percent error measures the accuracy of a measurement by comparing it to an accepted or true value. It shows how far off your measured value is from the accepted value, expressed as a percentage.
What is the difference between absolute and signed percent error?
Absolute percent error always gives a positive value, showing the magnitude of the error. Signed percent error can be positive or negative, indicating whether the measured value is above (positive) or below (negative) the accepted value.
How do I use this calculator?
Simply enter the measured value and the accepted value into the respective fields. The calculator will compute both the absolute and signed percent error for you.

Tips & Common Mistakes

Tips

  • Ensure both values are in the same units before calculating.
  • Use the signed percent error to see if your measurement is consistently high or low.
  • For most purposes, an absolute percent error below 5% is considered acceptable, but it depends on your field.
  • Double-check your accepted value – it should be the true or theoretical value.

Common Mistakes to Avoid

  • Entering the values in the wrong order – the measured value goes first, accepted value second.
  • Forgetting to use the same units for both values, which leads to incorrect results.
  • Misinterpreting the signed error as always positive – it can be negative if the measured value is less than the accepted value.

Last updated: August 13, 2026