80 g and 100 g
20 ÷ 90 × 100 ≈ 22.222222%
The absolute difference is 20 g and the arithmetic mean is 90 g. Reversing the order still gives the same percentage difference.
Measurements & comparisons
Percentage Difference Calculator
Compare two nonnegative values equally, using their arithmetic mean as the reference for the difference.
Calculate percentage difference
Percentage difference
Enter two values, then select Calculate.
- Absolute difference
- Arithmetic mean
The absolute difference and mean use your inputs' unit. Swapping the two values gives the same percentage.
Calculation steps and exact values
≈ marks display rounding. Calculations run in your browser. Press Enter to calculate. Successful results appear in this tab's Recent calculations.
Worked examples
12.5 and 12.5
0 ÷ 12.5 × 100 = 0%
Equal, positive values have no absolute or percentage difference. The average stays nonzero, so division is defined.
0 and 50
50 ÷ 25 × 100 = 200%
The difference is twice the mean. Under this formula, 200% is the largest percentage difference for nonnegative inputs.
Formula and calculation rules
Percentage difference = |A − B| ÷ ((A + B) ÷ 2) × 100
This calculator uses the average of the two inputs as the denominator, as described in the College of San Mateo physics introduction (PDF, page 1). The absolute value makes the comparison symmetric. The chosen convention accepts nonnegative numbers only; negative values are rejected rather than changing the denominator formula.
Both inputs cannot be zero: their average would be zero, making percentage difference undefined. One zero and one positive input give exactly 200%. Equal positive inputs give exactly 0%. All other accepted pairs give a result between 0% and 200%.
Use the same unit for both values and a scale with a meaningful zero. A percentage comparison of Celsius or Fahrenheit temperatures depends on the arbitrary zero of the scale; simply entering positive temperatures does not make that comparison meaningful.
Inputs accept at most 64 characters, 15 integer digits, and 10 decimal digits. Use a period for decimals and optional thousands commas. Units, expressions, fractions, and scientific notation are not accepted.
Calculations retain exact fractions until the final display rounding. Choose 0, 2, 4, 6, or 10 decimal places; halfway values round away from zero, and trailing zeros are omitted. ≈ marks every rounded value, including a nonzero result that displays as zero. Expand the calculation steps for exact fractions. Changing display precision does not add a recent-calculation entry.
This comparison describes the entered numbers. It does not establish measurement accuracy, uncertainty, statistical significance, or an acceptable difference for your application.
Common questions
How is percentage difference different from percentage change?
Percentage difference gives both values equal weight through their mean. Percentage change uses an original value as its baseline and preserves direction. From 80 to 100, the increase is 25%; from 100 to 80, the decrease is 20%. The symmetric percentage difference is about 22.222222% either way.
When should I use percent error instead?
Use percent error when comparing a measured value against an accepted, theoretical, or target reference. The reference determines that denominator. Use this percentage difference calculator when comparing two nonnegative values without designating either as the reference.
Can percentage difference exceed 100%?
Yes. For 10 and 50, the difference is 40 and the mean is 30, giving about 133.333333%. With the nonnegative inputs and mean denominator used here, the result cannot exceed 200%.
Why are two zeros or negative values rejected?
Two zeros would divide by a zero mean. Negative inputs are outside this calculator's chosen comparison rule. Definitions for signed data can use different denominators, so check the convention needed for your application instead of treating negative inputs as positive magnitudes.
Does ≈ 0% mean the values are identical?
No. The approximation mark means a small nonzero difference rounded to zero at the selected precision. An exact 0% has no approximation mark. Increase the display precision or inspect the exact calculation steps.
Is this a percentage-point difference?
No. If two rates are 20% and 30%, their percentage-point difference is 10 points. Entering 20 and 30 here gives a symmetric percentage difference of 40%, because 10 is 40% of their mean of 25.