Percent Error Calculator

Percent error is the absolute difference between the measured value and the true (accepted) value, divided by the true value, then multiplied by 100. In symbols: percent error = |measured - true| / |true| * 100. It expresses how far a measurement strays from the accepted reference as a percentage.

Percent error compares a measured value against a known true or accepted value, so it has a clear reference. Percent difference compares two values when neither is more correct than the other, dividing by their average. Use percent error in experiments with a known target and percent difference when comparing two equally valid measurements.

The standard definition uses the absolute value of the difference, so percent error is reported as a non-negative number. Some fields instead keep the sign to show whether the measurement was too high or too low. This calculator reports both the absolute percent error and the signed version so you can use whichever convention you need.

Percent error divides by the true value, so a true value of zero would require division by zero, which is undefined. When the accepted value is zero, percent error is not meaningful and you should use absolute error instead. This calculator returns n/a if the true value is zero.

A small percent error means the measurement is close to the accepted value, indicating good accuracy. A percent error of 1 percent means the measurement differs from the true value by one part in a hundred. The acceptable threshold depends on the field and the precision of the instruments involved.