Percent Error Calculator
Enter your measured value and the actual (accepted) value to find the percent error.
How percent error is calculated
Percent error is calculated as |measured value − actual value| / |actual value| × 100. The absolute value means the result is always positive, showing the magnitude of the discrepancy without indicating whether the measurement was too high or too low.
This is widely used in science and engineering to express how close an experimental or measured result is to the true or accepted value, normalized as a percentage so it's comparable across measurements of very different scales.
Frequently asked questions
What's a "good" percent error?
This depends entirely on the field and the precision of your instruments — a percent error under 1% might be expected for careful physics lab measurements, while a percent error under 10% might be perfectly acceptable for rougher field estimates.
What's the difference between percent error and percent difference?
Percent error compares a measured value against a known, accepted true value. Percent difference compares two measured values to each other when neither is established as the "correct" one — the formulas differ slightly in which value is used as the denominator.
Why use the absolute value in the formula?
Taking the absolute value ensures percent error is always reported as a positive number representing the size of the discrepancy, rather than a signed value that would indicate whether the measurement was an overestimate or underestimate.