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Percent Error Calculator

Compare a measured (experimental) value with the true (accepted) value to find the percent error and the absolute error — useful for labs and quality checks.

Percent error
2%

Absolute error |measured − true| = 0.2.

Quick answer

Percent error measures how far a measurement is from the accepted value: |measured − true| / |true| × 100. A reading of 9.8 against a true value of 10 gives |9.8 − 10| / 10 × 100 = 2%. This calculator shows both the percent error and the absolute error.

Formula & method

The tool takes the absolute difference between the measured and true values, divides by the absolute value of the true value, and multiplies by 100. Using absolute values keeps percent error non-negative, since it describes magnitude of error rather than direction. It is undefined when the true value is 0.

Examples

Example 1: Slightly low reading
Input
measured 9.8, true 10
Result
2%
Why
|9.8 − 10| / 10 × 100 = 0.2 / 10 × 100 = 2%.
Example 2: Slightly high reading
Input
measured 102, true 100
Result
2%
Why
|102 − 100| / 100 × 100 = 2%.
Example 3: Larger gap
Input
measured 48, true 50
Result
4%
Why
|48 − 50| / 50 × 100 = 2 / 50 × 100 = 4%.

When to use this tool

  • Reporting the accuracy of a lab measurement against an accepted value.
  • Checking instrument calibration or a manufacturing tolerance.
  • Comparing an estimate with the actual result.

Common mistakes

  • Dividing by the measured value instead of the true (accepted) value.
  • Forgetting the absolute value and reporting a negative percent error.
  • Confusing percent error (vs a known true value) with percent difference (between two measurements).

Frequently asked questions

What is the percent error formula?

Percent error = |measured value − true value| ÷ |true value| × 100. The absolute value makes it a non-negative measure of accuracy.

Why use absolute value?

Percent error describes the size of the discrepancy, not its direction, so it is conventionally reported as a positive number.

What is the true value?

The accepted, theoretical, or reference value you are comparing against — for example a textbook constant or a calibration standard.

What if the true value is 0?

Percent error is undefined because the formula divides by the true value, and division by zero has no meaning.

Is a smaller percent error better?

Yes. A smaller percent error means the measurement is closer to the accepted value, indicating better accuracy.

How is this different from percent difference?

Percent error compares a measurement to a known true value; percent difference compares two measured values and divides by their average.

Sources & references

External references open in a new tab. We are independent and not affiliated with these organizations.

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  • ✓ Formula and method shown above
Last updated: How we calculateReport a correctionDisclaimer

Provided “as is” for general information only — results may be inaccurate, so verify before you rely on them. No warranty; use at your own risk.

Built and reviewed by HIFreeTools against the formula shown above and any authoritative references cited on this page. See our methodology and editorial standards.

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