Percentage Error Calculator

Compare an observed value with an accepted or reference value

Your result will appear here.

About the Percentage Error Calculator

Percentage error compares an observed or experimental value with an accepted reference value. It expresses the size of the error relative to the reference, making results on different scales easier to compare.

The reference value matters because it is the denominator. If the accepted value is zero, the standard percentage-error formula is undefined.

How to Use the Percentage Error Calculator

  1. Enter the measured or experimental value.
  2. Enter the accepted, theoretical or reference value.
  3. Calculate the absolute error and percentage error.
  4. Keep the sign only if the calculator provides signed error and that direction is meaningful; ordinary percentage error is usually reported as a positive magnitude.

How the Calculation Works

Absolute error = |measured − accepted|. Percentage error = absolute error ÷ |accepted| × 100.

The accepted value provides the comparison scale, which is why a zero reference cannot produce an ordinary finite percentage error.

Worked example

Percentage Error Calculator Worked Example

Measured 49.2 when accepted value is 50

Absolute error = |49.2−50| = 0.8. Percentage error = 0.8÷50×100 = 1.6%.

Result guide

Understanding Your Percentage Error Calculator Result

A smaller percentage error means the measured value is closer to the accepted reference relative to that reference’s size. Whether a given error is acceptable depends on the field and measurement tolerance.

Before you rely on the answer

Assumptions and Limitations

  • The accepted value is the correct reference.
  • Measured and accepted values use the same units.
  • A zero accepted value requires a different error metric.

Practical tip

Using This Result in Practice

Report the measurement uncertainty separately when available. Percentage error describes disagreement with a reference, while uncertainty describes the precision limits of the measurement itself.

Related calculations

Useful Calculations to Continue With

If neither value should be treated as the accepted reference, use the Percentage Difference Calculator instead.

If you are comparing an old value with a new value over time, use the Percentage Change Calculator.

Common questions

Percentage Error Calculator FAQ

Why is percentage error usually positive?

The standard formula uses absolute error so it reports the size of the difference rather than its direction.

What if the accepted value is zero?

The standard percentage-error formula is undefined because it would require division by zero.

Is percentage error the same as percentage difference?

No. Percentage error uses an accepted reference, while percentage difference treats the two values more symmetrically.