This percent error calculator compares a measured or experimental value with the accepted true value. It is used in science labs and quality checks to show how far a measurement is from the real value.
Percent error formula
Percent error = |measured − true| ÷ |true| × 100
The absolute value makes percent error positive. The signed version, without absolute value on the top, shows whether your measurement was too high or too low.
Worked example
A student measures gravity as 9.6 m/s². The accepted value is 9.81 m/s². Percent error = |9.6 − 9.81| ÷ 9.81 × 100 ≈ 2.14%, and the measurement was too low.
Frequently asked questions
What is a good percent error?
It depends on the experiment. In many school labs, under 5% is considered good, but precise scientific work may need far less.
How is percent error different from percent change?
Percent error compares a measurement with a known correct value. Percent change compares an old value with a new one. For general percentages, use the percentage calculator.