Percent Error Calculator
Measure how far an experimental value is from the true value.
What percent error shows
Percent error tells you how far a measurement is from the accepted value, as a percentage of that accepted value. It is widely used in science labs to judge how accurate a result is.
The formula
Percent error = |observed − true| ÷ |true| × 100. The vertical bars mean the size of the difference, ignoring whether it is above or below.
Example
You measure gravity as 9.7 m/s² when the accepted value is 9.81. The error is 0.11, and 0.11 ÷ 9.81 × 100 = 1.12%.
If you want to know the change between two ordinary numbers rather than the error of a measurement, use the percentage change tab in the percentage calculator.
Frequently asked questions
Can percent error be negative?
In the usual formula, no, because it uses the absolute value. Some courses keep the sign to show over- or under-estimates, which is why the direction is shown separately.
What counts as a good percent error?
It depends on the experiment. Under 5% is often considered good in school labs, but precision work needs far less.
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