Calculate percent error, how far a measured or experimental value deviates from a known accepted value, expressed as a percentage.
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Percent Error = |Measured Value − Accepted Value| ÷ |Accepted Value| × 100. It's specifically used to express how far an experimental or measured result deviates from a known, accepted (true) value, always dividing by the accepted value, not the measured one. For example, measuring gravitational acceleration as 9.8 m/s² against the accepted 9.81 m/s² gives a percent error of about 0.10%.
Percent error assumes one of the two values (the accepted value) is authoritative, a known standard your measurement is being checked against. Our Percentage Difference Calculator instead compares two values symmetrically, with neither treated as more correct than the other, appropriate when you're simply comparing two measurements or estimates as peers.
Measuring gravitational acceleration as 9.8 m/s² against the accepted value of 9.81 m/s²: the absolute error is |9.8 − 9.81| = 0.01. Dividing by the accepted value and converting to a percentage: (0.01 ÷ 9.81) × 100 ≈ 0.1019%, meaning the measurement is off from the accepted value by about one-tenth of one percent.
Dividing by the measured value instead of the accepted value, percent error is always calculated relative to the accepted (true) value specifically, dividing by the wrong one gives a different, incorrect percentage.
Using percent error when neither value is actually a known standard, if you're comparing two peer measurements or estimates with neither being authoritative, use the Percentage Difference Calculator instead.
Assuming a small percent error always means the measurement is 'good enough', acceptable error thresholds vary enormously by field, a rough classroom experiment and a precision manufacturing process have very different standards for what counts as accurate.
This calculator uses the absolute value of the difference, so percent error is reported as a magnitude of deviation, regardless of whether the measured value was above or below the accepted value. The 'absolute error' figure shown alongside it is the raw (also absolute) numeric difference before converting to a percentage.
It depends entirely on the field and the precision of the measuring method, a percent error considered excellent in one context (say, a rough physical experiment) might be unacceptable in another (like precision manufacturing). There's no universal threshold.
If you're just comparing two values without either being an authoritative standard, use our Percentage Difference Calculator instead, which doesn't require designating one value as more correct than the other.
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