Percent error, sometimes referred to as percentage error, is an expression of the difference between a measured value and the known or accepted value. It is often used in science to report the difference between experimental values and expected values.

Example: Sam does an experiment to find how long it takes an apple to drop 2 meters. The theoretical value (using physics formulas) is 0.64 seconds.. But Sam measures 0.62 seconds, which is an approximate value.

Dr. Helmenstine holds a Ph.D. in biomedical sciences and is a science writer, educator, and consultant. She has taught science courses at the high school, college, and graduate levels.