Absolute and Relative Error Calculator
Compare a measured value to the true value: get absolute error, relative error and percent error in one step.
How it works
Absolute error = |measured − true| · Relative error = absolute ÷ |true| · Percent error = relative × 100
Absolute error is the raw size of a mistake in the same units as the measurement, while relative error scales that gap against the true value so you can compare accuracy across very different magnitudes. A 1 cm miss matters far more on a 10 cm object than on a 10 m one, and relative error captures exactly that. Multiplying relative error by 100 gives the familiar percent error used in lab reports.
Worked example
A pendulum gives g = 9.8 m/s² against an accepted 9.81 (here shown with a true value of 10). The absolute error is |9.8 − 10| = 0.2, the relative error is 0.2 ÷ 10 = 0.02, and the percent error is 2%.
Sources: Approximation error — Wikipedia
Frequently asked questions
What is the difference between absolute and relative error?
Absolute error is the plain difference between measured and true values, carrying units. Relative error divides that by the true value, giving a unitless fraction that fairly compares accuracy between measurements of different sizes.
Why is my relative error undefined?
Relative and percent error divide by the true value, so they are undefined when the accepted value is exactly zero. Only the absolute error is meaningful in that case.
Is percent error ever negative?
By this convention no — the absolute value removes the sign, so percent error only reports the size of the discrepancy. If you need direction, compare measured minus true directly to see whether you over- or under-shot.
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This calculator is for educational purposes. Double-check important results before acting on them.