Percent Difference Calculator

Percent difference measures how different two values are, relative to their average. The formula is: |V1 - V2| / ((V1 + V2) / 2) x 100%. It is always positive and symmetric, meaning the order of the values does not affect the result.

Percent change measures directional change FROM an original TO a new value, using the original as the reference. Percent difference compares two values without a reference point, using their average. Use percent change when you have before/after; use percent difference when comparing two measurements.

Percent error compares a measured value to a known/accepted value (the "truth"). Percent difference compares two values where neither is considered "correct" - for example, comparing two experimental measurements. Error uses theoretical value as denominator; difference uses average.

The formula works best with positive values because the mean (average) is used as the reference. If values have opposite signs, the mean could be zero or very small, leading to extremely large or undefined percent differences. The formula is designed for comparing magnitudes.

The percent difference approaches 200% as one value approaches zero while the other remains positive. For example, comparing 0.001 and 100: the difference is large relative to the mean. If both values are identical, percent difference is 0%.