Percent Error Calculator

About this calculator

This calculator compares a measured (experimental) value against a known or accepted (theoretical) value and expresses the difference as a percentage of the theoretical value — the standard formula |measured − theoretical| / theoretical × 100 used to judge how accurate a measurement or estimate is.

It's a staple of school and university science labs, where a chemistry, physics or biology experiment's measured result (say, a boiling point or a measured density) is compared against the textbook or accepted value to judge how well the experiment went. It's also used more broadly in quality control and forecasting, wherever someone needs to quantify how far an estimate or reading strayed from the true or expected figure.