Last updated September 26, 2026 · Report an error
Percent error measures how far a measured or calculated result is from the true or accepted value — a standard way to express the accuracy of an experiment or measurement.
This calculator finds the percent error between an experimental value and a theoretical value, showing the full working.
How it works
Enter the experimental (measured) value and the theoretical (accepted) value. The calculator finds the absolute difference between them, divides by the absolute theoretical value, and expresses the result as a percentage.
- Enter experimental (measured) value.
- Enter theoretical (accepted) value.
- Click Calculate to see your results.
Examples
Measuring gravitational acceleration
A measured value of 9.8 m/s² against the accepted 9.81 m/s² gives a percent error of about 0.10%.
Who should use it
- Evaluating the accuracy of a science lab measurement.
- Comparing a calculated engineering estimate against a known specification.
Industry applications
- Science education and laboratory work
- Engineering and quality control measurements
Advantages
- Handles the full percent error formula, including the absolute value step.
- Shows the formula, substitution, and final result separately.
Limitations
- Requires a nonzero theoretical value, since the formula divides by it.
Common mistakes to avoid
- Dividing by the experimental value instead of the theoretical (accepted) value — the accepted value is always the denominator.
- Forgetting to take the absolute value of the difference, which would let the sign of the error skew the interpretation.
Best practices
- Report percent error alongside your raw measured and accepted values, not on its own, so readers can judge the context.
Tips
- If you're comparing two measurements where neither is a known "true" value, use percent difference instead of percent error.
Frequently asked questions
Yes, with no signup and no limit on how many calculations you run.
It depends entirely on the field and experiment — some contexts expect well under 1%, while others accept 10% or more. Check your course or field's standards.
Percent error compares a measured value to a known, accepted true value. Percent difference compares two measured values where neither is known to be more correct — it divides by the average of the two instead.
This calculator always reports percent error as a positive value (using the absolute difference), which is the standard convention — it reports magnitude, not direction of error.