Percent Error Calculator
Find the percent error between a measured value and the accepted true value, with the absolute and signed error.
How it works
percent error = |measured − true| ÷ |true| × 100
Percent error measures how far a measured or estimated value falls from the accepted true value, scaled to the size of that true value. Take the absolute difference between the two, divide by the absolute true value, and multiply by 100. Because it divides by the true value, the same absolute miss counts as a larger error when the true value is small.
Worked example
A measurement reads 9.8 where the accepted value is 10. The percent error is |9.8 − 10| ÷ |10| × 100 = 0.2 ÷ 10 × 100 = 2%, so the reading is off by one part in fifty.
Frequently asked questions
What does percent error tell me?
How far a measured or estimated value lands from the accepted true value, as a percentage of that true value. Smaller is better — a 2% error means the measurement is off by one part in fifty.
Should percent error ever be negative?
The standard definition uses the absolute difference, so it is never negative. If you care about direction, the signed error (measured minus true) shows whether you overshot or undershot.
What’s the difference between percent error and percent difference?
Percent error compares a measurement against a known correct value. Percent difference compares two measurements when neither is the accepted truth, dividing by their average instead.
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This calculator is for educational purposes. Double-check important results before acting on them.