Formula
How percent difference is calculated
Percent difference =|value 1 − value 2| ÷ ((|value 1| + |value 2|) ÷ 2) × 100
Find the absolute difference between the two measurements. Divide it by the average magnitude of both values, then multiply by 100.
Worked example
Percent difference example
Two experimental measurements are 10 units and 12 units.
- Find the absolute difference: |10 − 12| = 2
- Find the average magnitude: (10 + 12) ÷ 2 = 11
- Divide: 2 ÷ 11 = 0.181818...
- Multiply by 100: 0.181818 × 100 = 18.1818%
Important distinction
Percent difference vs. percent error
Use percent difference when neither measurement is treated as an accepted reference. Use percent error when one value is experimental and the other is a trusted accepted or theoretical value.
Need to compare a measurement with a reference value? Use the Percent Error Calculator.
Interpretation limits
Assumptions and limitations
Percent difference is intended for comparing two experimental values when neither value is treated as the accepted reference. Both measurements should represent the same quantity and use compatible units.
The percentage can become unstable when the average magnitude is close to zero, and it does not explain whether a difference was caused by random variation, systematic error, or an unsuitable measurement method.
Related tools
Related measurement calculators
Compare an experimental result with an accepted value using the Percent Error Calculator.
Evaluate uncertainty across calculated quantities with the Uncertainty Propagation Calculator.
Questions and answers
Percent difference FAQ
What is the difference between percent difference and percent error?
Percent difference compares two measured values using their average as the denominator. Percent error compares an experimental value with an accepted or theoretical value.
Can percent difference be greater than 100 percent?
Yes. Percent difference can exceed 100 percent when two values are far apart relative to their average magnitude.
Why is percent difference undefined when both values are zero?
When both values are zero, their average is also zero. The formula would require division by zero, which is undefined.