CalcCommonsHow to use
Enter the observed measurement and its reference in the same unit. Calculate to see magnitude and direction separately. Do not enter a percentage sign or a unit in the numeric fields.
For related tasks, try the Percentage Calculator.
Formula & how it works
Percent error = |measured − reference| ÷ |reference| × 100%.
Worked examples
Example 1
A measured value of 98 and reference of 100 give |98−100|/100×100 = 2% error. The measured value is lower.
Example 2
A measured value of −9 and reference of −10 give 10% error; the signed difference is +1.
Assumptions & practical notes
Use the same units for both values. The reference is the accepted or target value for your task.
Percentage error is undefined when the reference is zero. Absolute error still has meaning, but cannot be expressed using this relative formula.
See our calculation methodology for unit definitions and testing practices.
Frequently asked questions
Can error exceed 100%?
Yes. It happens when the absolute deviation exceeds the magnitude of the reference.
Is this percent difference?
No. Percent difference compares two observations without treating one as the reference, usually using their average as the denominator.
Why is the percentage nonnegative?
The formula uses absolute values. Read Signed difference and Direction to tell whether the measurement is above or below the reference.
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