How it works
The absolute difference between the two values is divided by their average, then multiplied by 100. Neither value is treated as the "original", so entering them in the opposite order gives the same result.
Formula: Percentage difference = |a − b| ÷ ((a + b) ÷ 2) × 100
Examples
Two measurements
8 and 12 differ by 4, which is 40% of their average of 10.
Things to keep in mind
- Percentage difference is symmetric and always zero or positive — unlike percentage change, it does not say which value increased or decreased relative to the other. See the Percentage Change Calculator when direction matters.
- Both values must be zero or more. Percentage difference compares the size of two quantities, which is not a meaningful comparison for a negative quantity, so negative input is rejected rather than producing a sign-dependent result.
- The two values cannot both be zero, since their average would be zero and there would be nothing to express the difference as a percentage of.