The Percentage Error Formula
Percentage Error = |Experimental − Theoretical| ÷ |Theoretical| × 100
Why We Use Absolute Value
Percentage error is conventionally expressed as a positive number regardless of whether your experimental value is above or below the theoretical value — the absolute value ensures the result reflects magnitude of error, not direction.
Common Uses
- Physics and chemistry lab reports, comparing measured results to accepted scientific values
- Quality control, comparing actual measurements to specifications
- Evaluating the accuracy of an estimate or prediction against the actual outcome
What Counts as "Good" Accuracy?
Acceptable percentage error varies enormously by field and context — some scientific measurements demand well under 1% error, while other estimates might reasonably tolerate 10-20% error. Context always determines the acceptable threshold.