Percent Error Calculator

About this calculator

Percent error compares a measurement to the accepted true value: take the difference, divide by the true value, and express it as a percentage — conventionally as an absolute (positive) number. Measuring 9.8 when the true value is 10 is a percent error of 2%.

It's the standard way to report accuracy in lab work because it puts errors on a common scale: being off by 2 grams matters a lot when the true value is 10 grams (20%) and barely at all when it's 10 kilograms (0.02%).

The true value must not be zero — percent error is undefined there, and comparisons near zero can be misleading even when defined.