Percent Error Calculator
Measure how far an experimental or estimated value is from the true or accepted value, as an absolute error and a percentage.
Percent error compares a measured value with the accepted value: |measured − accepted| ÷ |accepted| × 100.
How the percent error calculator works
Percent error compares a measured value with the accepted value: |measured − accepted| ÷ |accepted| × 100. It is used in science classes and quality control to judge accuracy. The relative error is the same ratio without the ×100; the absolute error is the plain difference.
Formula: percent error = |measured − accepted| / |accepted| × 100
Worked examples
| Inputs | Percent error | Note |
|---|---|---|
| g measured 9.6 vs 9.81 | 2.141% | a 2.1% error |
| 105 vs 100 | 5% | 5% over |
FAQFrequently asked questions
Can percent error be negative?
By the usual definition no — it uses the absolute difference. Some teachers keep the sign to show direction; the direction row here does that.
What is a good percent error?
It depends on the experiment: under 5% is typical for school physics; industrial tolerances can be far tighter.
What if the accepted value is zero?
Percent error is undefined; use the absolute error instead.
Is percent error the same as percent difference?
No — percent difference compares two measurements symmetrically, dividing by their average, when neither is the accepted value.
How is relative error different?
Relative error is the same ratio expressed as a decimal (0.021) rather than a percentage (2.1%).
Where these figures come from
- NIST Digital Library of Mathematical Functions — reference definitions for elementary and special functions
- Wolfram MathWorld — definitions and formulas for every topic on this page
- NIST/SEMATECH e-Handbook of Statistical Methods — the statistical formulas (mean, variance, z, confidence intervals, sample size)
- National curriculum in England — Mathematics — the terms and methods taught in UK schools
Last checked: September 2026. Formulas are fixed by mathematics and do not change with tax years or regulations.