Percent Error Calculator

How This Calculator Works

Percent error measures how far a measured (experimental) value is from a known, accepted (theoretical) value, expressed as a percentage. It’s the standard way science labs and measurement-based fields report how accurate a result was. Enter both values, and this calculator finds the percent error instantly.

The Formula

$$\text{Percent Error} = \frac{\left|\vA{\text{Experimental}} - \vB{\text{Theoretical}}\right|}{\left|\vB{\text{Theoretical}}\right|} \times 100$$

The result is always reported as a positive percentage — percent error measures the SIZE of the error, not its direction. Whether your experimental value came in above or below the theoretical one, this calculator’s analysis notes which way it went.

Worked Example

An experiment measures a value of 48, when the accepted theoretical value is 50:

1. Difference: $48 - 50 = -2$
2. Percent error: $|-2| \div |50| \times 100 = 4\%$

Percent Error vs. Percent Difference

Percent error and percent difference sound similar but answer different questions. Percent error compares a measurement against a known, accepted “correct” value — use it whenever you have a true or theoretical value to compare against. Percent difference (available on this site’s Percentage Calculator) instead compares two measurements to each other with no assumption that either one is “correct,” dividing by their average rather than a single accepted value.