Percent Error Calculator
Enter your measured value and the accepted value to see how far off you were, as a percentage.
This result is an estimate only. Double-check important figures before relying on them.
How it is calculated
- Absolute error = |measured − actual|
- Percent error = absolute error ÷ |actual| × 100
- Signed percent error = (measured − actual) ÷ |actual| × 100
To compare two values with no true one, use the percentage difference calculator.
Worked example
You measure 9.5 where the true value is 10:
- Absolute error = 0.5
- Percent error = 0.5 ÷ 10 × 100 = 5%
- Signed error = −5%
Why your number may differ
Some textbooks drop the absolute value and report the signed result. Others write the error as a decimal. Check which your teacher or lab sheet wants.
Frequently asked questions
What is the percent error formula?
Percent error = |measured − actual| ÷ |actual| × 100. It tells you the size of the error relative to the true value.
What does the signed error mean?
A negative sign means you measured below the true value, and a positive sign means above it.
Why can the actual value not be 0?
The error is divided by the actual value, and dividing by zero has no answer.