What is percent difference?
Percent difference compares two numbers without treating either one as the starting point. It measures the gap against the midpoint between them (their average), so you get the same answer whichever number you put first. That suits two measurements, two quotes or two test results.
How to calculate percent difference
Here it is with your numbers:
- Find the difference, ignoring any minus sign: 9.95 − 10.2, which is 0.25.
- Find the average of the two values: (9.95 + 10.2) ÷ 2 = 10.075.
- Divide the difference by the average: 0.25 ÷ 10.075 = 0.0248.
- Multiply by 100 to turn it into a percent: 2.48%.
It means the two values differ by 2.48% of their average. From 9.95, 10.2 is 2.51% higher. From 10.2, 9.95 is 2.45% lower.
With negative numbers we divide by the size of the average (without its minus sign), so a percent difference is never negative: −10 and −5 differ by 66.67%. Some calculators show −66.67% or refuse negative numbers.
Source NC State University · Percent error and percent difference (physics lab manual) ↗
Percent difference vs percent change vs percent error
These three are often mixed up. The only thing that changes is what you divide by: the average, the starting value, or the accepted value. Here are your two numbers measured each way:
| Measure | When to use it | Your numbers |
|---|---|---|
| Percent difference | Neither is the starting point | 2.48% |
| Change from 9.95 to 10.2 | 9.95 is the "before" | +2.51% |
| Change from 10.2 to 9.95 | 10.2 is the "before" | −2.45% |
Use percent error (the switch above the calculator) when one value is the accepted or correct one, like a textbook figure you measured in a lab.
Source Microsoft Support · Calculate percentages ↗
Percent difference examples
| Values | Difference | Percent difference |
|---|---|---|
| 9.95 and 10.2 | 0.25 | 2.48% |
| 10 and 20 | 10 | 66.67% |
| $450 and $500 quotes | $50 | 10.53% |
Percent difference in Excel
| To find | Formula |
|---|---|
| Percent difference | =ABS(A2-B2)/AVERAGE(A2,B2) |
| Percent error | =ABS(B2-A2)/B2 |
For percent error, put the measured value in A2 and the accepted value in B2. Format the answer cell as Percentage.
FAQs
How do you calculate percent difference?
Divide the difference between the two numbers by their average, then multiply by 100. For 9.95 and 10.2: the difference is 0.25, the average is 10.075, and 0.25 ÷ 10.075 × 100 is about 2.5%.
Source NC State University · Percent error and percent difference (physics lab manual) ↗
How do you find the percent difference between two numbers?
Use the same formula whichever number comes first; the answer is the same both ways round. If one number is clearly the "before", use percent change instead: 10 to 20 is a 100% rise, while their percent difference is 66.67%.
What's the difference between percent error and percent difference?
Percent error compares a measurement with an accepted value and divides by that accepted value. Percent difference compares two values when neither is "correct" and divides by their average.
How do you calculate percent difference in Excel?
With the two values in A2 and B2, type =ABS(A2-B2)/AVERAGE(A2,B2) and format the cell as a percentage. ABS removes the minus sign; AVERAGE finds the midpoint.
Sources
- NC State University: Percent error and percent difference (physics lab manual)
- Microsoft Support: Calculate percentages