Percent Error Calculator
Compare a measured value with the true value and find the percent error.
How far the measured value is from the actual value, as a percentage.
2%
errorError
2%
Accurate
98%
- 1
Absolute error
|98 − 100| = 2 - 2
Relative error
2 ÷ |100| = 0.02Dividing by the actual value scales the error relative to the true size of the quantity. - 3
Percent error
0.02 × 100 = 2
Formula
How this is calculated
This calculator takes two numbers in the same units: the measured (experimental) value you obtained, and the actual (true or accepted) value you are comparing against. The order of subtraction does not matter because the result is wrapped in absolute-value bars.
First it finds the absolute error, the size of the gap between the two values: |measured − actual|. This is reported in the original units. It then divides that gap by the absolute value of the actual value, which scales the error relative to how large the true quantity is, and multiplies by 100 to express it as a percentage. Using |actual| in the denominator keeps the result positive even when the accepted value is negative.
The percentage is purely about accuracy (closeness to the true value); it says nothing about precision or repeatability. The calculation assumes the actual value is exact and error-free. It is undefined when the actual value is 0, since dividing by zero has no meaning, so that case is flagged rather than computed.
Examples
| Input | Result |
|---|---|
| measured = 98, actual = 100 | percent error = 2% |
About this calculator
Percent error measures how close an experimental or measured value is to the true, accepted value. It is the absolute difference between the two divided by the absolute value of the actual value, multiplied by 100 to express it as a percentage. A smaller percent error means a more accurate measurement.
This calculation is a staple of science labs in chemistry and physics, where you compare your experimental result against a known reference. The absolute value bars ensure the percent error is always reported as a positive number, regardless of whether your measurement was too high or too low.
Frequently asked questions
Subtract the actual value from the measured value, take the absolute value, divide by the absolute value of the actual value, then multiply by 100.
No. Because the formula uses absolute values, percent error is always reported as a non-negative percentage, even if the measurement was below the true value.
It depends on the experiment, but in many school labs a percent error under about 5% is considered accurate. Lower is always better.
Also known as
TG we-Calculate Editorial Team. (2026). Percent Error Calculator [Online calculator]. TG we-Calculate. https://we-calculate.com/calculator/percent-error-calculator
TG we-Calculate Editorial Team. "Percent Error Calculator." TG we-Calculate. 2026. https://we-calculate.com/calculator/percent-error-calculator.
TG we-Calculate Editorial Team, "Percent Error Calculator," TG we-Calculate, 2026. [Online]. Available: https://we-calculate.com/calculator/percent-error-calculator
@misc{wecalculate_percent_error_calculator, title = {Percent Error Calculator}, author = {{TG we-Calculate Editorial Team}}, howpublished = {\url{https://we-calculate.com/calculator/percent-error-calculator}}, year = {2026}, note = {TG we-Calculate} }
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