Percentage Error Calculator
Calculate percentage error between an estimated or measured value and the actual value.
About the % Error Calculator
Percentage error is a standard measurement used in science, engineering, and statistics to express how far an estimated or measured value strayed from the true or accepted value, always as a positive percentage of the true value.
How It Works
The calculator subtracts the actual value from the estimated value, takes the absolute value of that difference, then divides by the absolute value of the actual figure and multiplies by 100.
Percentage Error (%) = |Estimated − Actual| / |Actual| × 100.
Worked example
Scenario: A measurement of 98 when the accepted value is 100.
- Absolute error: |98 − 100| = 2.
- Percentage error: 2 ÷ |100| × 100 = 2%.
Result: A 2% error.
Interpreting percentage error
Percentage error compares an observed or estimated value with an accepted or actual value. It expresses the size of the error relative to the accepted value, which makes errors easier to compare across different scales.
Tips and common mistakes
- Percentage error uses the true value as the baseline, so the actual value cannot be zero.
- Report the sign separately if direction matters: 98 is 2% low.
- Lab reports often treat errors under 5% as acceptable, but the standard depends on the instrument.
Assumptions & Limitations
- Assumes the 'actual' value is the accepted true or reference value, and the 'estimated' value is what was measured or predicted.
- The result is always reported as non-negative, since percentage error measures the size of the deviation, not its direction.
- If the actual value is zero, percentage error is mathematically undefined since you cannot divide by zero.