How it’s calculated
Percent error measures how far a measurement is from the accepted value, as a percentage of the accepted value. It describes accuracy (closeness to the true value), not precision (agreement between repeat measurements).
Example: a pendulum experiment gives g = 9.60 m/s² against the accepted 9.81 m/s². Error = |9.60 − 9.81| ÷ 9.81 × 100% = 0.21 ÷ 9.81 × 100% = 2.14% (measurement low).
Frequently asked questions
Can percent error be negative?
The usual definition takes the absolute value, so it is never negative. The signed version shown here tells you whether your measurement was high (+) or low (−).
What is a good percent error?
It depends on the experiment. In introductory labs, under about 5% is often considered good; precision measurements aim for far less.
How is this different from percent difference?
Percent error compares to a known accepted value. Percent difference compares two measurements with no reference, dividing by their average.
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Sources
- Introductory Chemistry (CK-12), §3.13 Percent Error — LibreTexts
- Chemistry 2e, §1.5 Measurement Uncertainty, Accuracy, and Precision — OpenStax
Formulas are taken from the free public references above. Results are provided “as is” for informational and educational purposes only. See our disclaimer.
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