How this calculator works
Take the absolute gap between the measurement and its accepted reference, then divide by the absolute reference value. Express that fraction as a percentage. Both absolute values matter: this calculator reports the magnitude of the error even when the reference is negative.
Formula
Percent error = |measured - accepted| / |accepted| × 100%.
Worked example
A measured value of 22 compared with an accepted value of 20 is 2 units away, giving 10% error. A measurement of 47 against 50 gives 6%.
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Frequently asked questions
Can percent error be negative?
This absolute-error calculation is always non-negative. A signed relative error is a different convention that also shows whether the measurement is above or below the reference.
Why is a zero reference rejected?
Relative error divides by the reference magnitude. At zero that ratio is undefined; an absolute error in the original units may still be useful.
Does it matter whether I measured above or below the accepted value?
No. The page uses the absolute gap, so 18 against 20 gives the same 10% error as 22 against 20.