Percent error calculator
The percent error between a measured value and the true value.
About this calculator
This percent error calculator compares a measured or experimental value with the true or accepted value, and shows how far off it is as a percentage.
It's a standard step in science lab reports and quality checks.
How it works
Percent error = |measured − true| ÷ |true| × 100. The signed error keeps the sign, so you can see whether the measurement was too high or too low.
Last reviewed:
Worked example
- Measured value: 9.6
- True value: 9.81
Percent error: 2.1407%
Common questions
What is a good percent error?
It depends on the experiment. In a school lab, under 5% is often seen as good, while precise scientific work aims for much less.
Can percent error be negative?
The usual formula uses the absolute value, so it is always positive. The signed error shows whether you were over or under.
What is the difference between percent error and percent change?
Percent error compares a measurement with a known true value. Percent change compares a new value with an old one.
The story behind it
Where the idea came from: Scientists began reporting measurement errors carefully in the 1700s and 1800s, as astronomy and surveying demanded ever more accuracy.
Knowing how far a result is from the truth is what turns a measurement into science. Percent error makes that comparison simple, whatever the units or size of the quantity.
Why you can trust this calculator
- It runs in your browser. Nothing you type into it is sent anywhere.
- The method is explained on this page, so you can check it yourself.
- Free to use, with no sign-up.
- Results are estimates, so please double-check anything important.
- Spotted a mistake? Tell us and we'll look into it.
After 15 years as a mathematics educator, I built CalculStore to give students, teachers, professionals and anyone working with numbers simple, reliable tools.
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