Coefficient of Variation Calculator
Compute the coefficient of variation (CV) — standard deviation as a percentage of the mean — to compare relative spread across data sets.
How it works
CV = standard deviation ÷ mean × 100%
The coefficient of variation expresses the standard deviation as a percentage of the mean, giving a unitless measure of relative spread. Because it strips out the scale, it lets you compare the consistency of data sets with different units or wildly different averages. It only makes sense on a ratio scale — data with a meaningful zero and positive values — since a mean near zero makes the ratio explode.
Worked example
A data set with mean 50 and standard deviation 10 has CV = 10 ÷ 50 × 100 = 20%. A second set with mean 500 and standard deviation 50 also has CV = 10%, so despite the far larger raw spread it is actually more consistent relative to its size.
Frequently asked questions
When is the CV more useful than the standard deviation?
When comparing spread across data measured differently — say, weight variation in grams versus in pounds, or salaries versus test scores. The raw standard deviations aren’t comparable, but the CV percentages are.
Why can’t I use the CV when the mean is near zero?
Dividing by a mean close to zero produces an enormous, unstable CV, and a negative mean makes the sign meaningless. That is why the CV is reserved for ratio-scale data with a positive mean, like heights, prices or reaction times.
What counts as a high coefficient of variation?
It depends on the field, but a rough guide is that under about 15% is low variability, 15–30% is moderate, and above 30% is high. Always judge it against norms for your specific measurement.
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For education — check assumptions (sample size, distribution) before using statistics in real decisions.