Percentage Error Calculator
For chemistry and physics labs: enter your measured value and the accepted value to get the percent error, the absolute error, and the signed error that tells you whether you measured high or low.
- Percent error
- 2.1407%
- Absolute error
- 0.21
- Signed error
- -2.1407%
Steps
- |9.6 − 9.81| = 0.21
- 0.21 ÷ |9.81| × 100 = 2.1407%
Worked example
Example: measuring gravity as 9.6 m/s² (accepted 9.81 m/s²)
- |9.6 − 9.81| = 0.21
- 0.21 ÷ 9.81 = 0.02141
- × 100 = 2.14%
Your percent error is about 2.14% (you measured low).
Formula
Percent error = |Measured − Accepted| ÷ |Accepted| × 100
Most teachers want the absolute value, so percent error is never negative. The signed version keeps the direction.
Frequently asked questions
What is a good percent error?
It depends on the experiment, but in school labs under 5% is usually considered good and under 1% excellent.
Can percent error be negative?
With the standard absolute-value formula, no. Without it, a negative result means your measurement was below the accepted value.
What's the difference between percent error and percent difference?
Percent error compares to a known true value. Percent difference compares two measurements to their average when neither is known to be correct.
Last reviewed October 17, 2026 · Calculations run in your browser; nothing you enter is sent to a server.