Percent Error Calculator - Measured vs. Accepted Value
Calculate percent error between a measured/experimental value and a theoretical/accepted value.
Percent Error
4.000%
Underestimate by 4.000%
How to Calculate Percent Error
Percent error measures how far an experimental or measured value deviates from the theoretical or accepted value, expressed as a percentage of the accepted value. It's a standard way to quantify accuracy in a lab measurement, calculation, or estimate.
Example
If a student measures the boiling point of water as 98°C when the accepted value is 100°C, the percent error is |98 − 100| / 100 × 100 = 2%. The measured value is below the accepted value, so it's described as a 2% underestimate.
Common Use Cases
- Evaluating accuracy in science lab experiments against known reference values.
- Comparing an estimate, forecast, or model prediction to the actual outcome.
- Quality control checks comparing a measured value to a specified target.
FAQs
What's the difference between percent error and percent difference?
Percent error compares a measured value against a known, accepted, or theoretical value — treating one value as the "truth." Percent difference instead compares two measured values of equal standing, with neither treated as more correct than the other.
Can percent error be negative?
The standard definition uses an absolute value, so percent error itself is always zero or positive. This calculator also shows the signed version so you can see whether your measured value overestimated or underestimated the accepted value.
What counts as a "good" percent error?
It depends entirely on the context — a percent error under 5% is often considered good in many school science experiments, but precision manufacturing or analytical chemistry may require far smaller errors, sometimes well under 1%.