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How It Works
Percent difference measures how far apart two values are relative to their average. Unlike percent change, neither value is treated as the “original.” The absolute value in the numerator ensures the result is always positive.
Example Problem
Two lab instruments measure a sample at 48.2 and 50.5. What is the percent difference?
- Difference: |48.2 − 50.5| = 2.3
- Average: (48.2 + 50.5) / 2 = 49.35
- Percent difference: (2.3 / 49.35) × 100 = 4.66%
Frequently Asked Questions
What is the difference between percent difference and percent error?
Percent difference treats both values equally and divides by their average. Percent error compares a measured value against a known, accepted value. Use percent difference when neither measurement is the “correct” one.
Can percent difference be negative?
No. The formula uses an absolute value in the numerator, so the result is always zero or positive. A percent difference of 0% means the two values are identical.
When should I use percent difference in a lab report?
Use it when comparing two independent experimental results where neither is the accepted standard. For example, if two students measure the density of the same metal and get 7.8 and 8.1 g/cm³, the percent difference is about 3.8%.
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