Percent difference

Percent difference, also referred to as percentage difference, is another measure used to compare two values. It is similar to percent change and percent error (refer below for more detail). The equation for percent difference is:

Where V1 and V2 are two values being compared.

When measuring percent difference, the order of the two values (V1 or V2) in the formula doesn't matter. This is because percent difference is used for values that should not be distinguishable in such a way that one value would stand out to be used as a reference over the other (as is the case when using the percent error/change formulas). Percent difference may be used to compare two heights, ages, hours worked, or other numbers.


1. If John is 5 feet 8 inches tall (172.72 cm) and James is 6 feet 2 inches tall (187.96 cm), what is the percent difference between their heights?

Plugging 172.72 in for V1 and 187.96 in for V2,

2. If Katie ran 1900 meters and Blake ran 1500 meters, what is the percent difference between the distances they ran?

Since we use the absolute value for the difference, the order of the values does not matter. In either of the examples above, we could've switched which value was used for V1 and V2, and the result would have been the same.

Percent difference, percent change, and percent error

These three measures, though similar, are not interchangeable. They are used in different contexts.

Percent difference

Percent change

Percent change assumes that there is an "old" and a "new" value and compares values relative to the old value. So, the reference value is the old value, and percent change is used to determine whether the new value is the same, an increase, or a decrease, relative to the old value.

Percent error

Percent error is mostly used in more scientific settings. In the context of experiments, percent error is used when there is some known/theoretical value being compared to an experimental value.

So, in all three measures, we are comparing the difference between two values to some reference value. The difference between the three is what the reference value is, which affects which of these measures we choose to use.