Calculate percentage error
Compare a measured value with a nonzero reference value. See the size of the error and whether the measurement is above or below the reference.
Calculations run in your browser. The values you enter are not uploaded or stored by this tool.
How it works
- Enter the measured or experimental value.
- Enter the reference, accepted or theoretical value in the same units.
- Read percentage error, signed error and absolute error, then copy the results.
Percentage error formula
Percentage error = |measured − reference| ÷ |reference| × 100. Signed error = measured − reference. Absolute error is the magnitude of that difference. A measurement of 98 against a reference of 100 has signed error −2, absolute error 2 and percentage error 2%. Use the same units for both inputs.
Negative values and zero references
A negative reference is valid here: its absolute magnitude is used as the denominator. Measured −45 against reference −50 gives signed error 5 and percentage error 10%. A zero reference makes percentage error undefined, including when the measured value is also zero, so no result is shown.
Error is different from percentage change
Percentage error compares a measurement with a chosen reference and reports a nonnegative percentage. Percentage change compares an old and a new value and retains a direction. Neither calculation establishes whether a measurement is sufficiently accurate for your experiment. Results use browser floating-point arithmetic; overflowing calculations are rejected, and displayed results are rounded to eight decimal places or scientific notation for very small or large values.
Worked examples
| Measured | Reference | Signed error | Absolute error | Percentage error |
|---|---|---|---|---|
| 98 | 100 | -2 | 2 | 2% |
| 22 | 20 | 2 | 2 | 10% |
| -45 | -50 | 5 | 5 | 10% |
| 1 | 3 | -2 | 2 | 66.6667% |
Frequently asked questions
Can percentage error exceed 100%?
Yes. Measured 50 against reference −50 has absolute error 100. Dividing by the reference magnitude of 50 gives 200%.
What if my measured value is below the reference?
The signed error is negative, while absolute error and percentage error stay nonnegative. Measured 98 against reference 100 gives −2 signed error and 2% percentage error.
Can I enter a fraction?
Convert the fraction to a decimal before entering it. For measured 1 and reference 3, the exact percentage error is 200/3%, displayed as approximately 66.66666667%.
Does this enforce significant figures?
No. It calculates from the entered values and rounds for display. Apply your laboratory or reporting rules for significant figures separately.
Sources
Last reviewed: October 18, 2026
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