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Coefficient of Variation Calculator

Measure relative variability by dividing the standard deviation by the mean.

How it is calculated

The tool divides the standard deviation by the mean and expresses the ratio as a percentage: CV = SD / mean × 100. Both SD and mean must be in the same unit (for example kg, ms or dollars), and that unit cancels out, which is why the CV is unitless. The tool also shows the plain ratio SD / mean.

If the mean is 0 the tool returns no result, because the ratio is undefined. A negative standard deviation is rejected as well. A negative mean is not rejected and gives a negative CV, which is hard to interpret, so the CV is best used for data measured on a ratio scale with a positive mean.

Worked example

Suppose a batch of parts has a mean weight of 50 g and a standard deviation of 7.5 g. First the ratio: 7.5 / 50 = 0.15. Then multiply by 100: 0.15 × 100 = 15.00%. The result is 15.00%, so the typical spread is 15% of the average weight.

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Common mistakes

  • Entering the variance instead of the standard deviation; the variance is the square of the SD and gives a far larger, meaningless CV.
  • Mixing units, such as a mean in kilograms and an SD in grams, which makes the CV wrong by a factor of 1000.
  • Using the CV on interval-scale data such as temperature in Celsius, where the mean can sit near zero and the CV explodes or changes with the choice of zero point.
  • Typing the mean as 0 or leaving a field empty and expecting a number; the tool returns nothing in that case.
  • Reading the ratio 0.15 as 0.15% rather than 15%.

About this calculator

This calculator finds the coefficient of variation (CV): CV = (standard deviation / mean) × 100%. Unlike standard deviation alone, CV is a unitless, scale-independent measure of spread, so it lets you compare the relative variability of datasets that have different units or very different means — something raw standard deviation cannot do.

Statisticians, analysts, and lab scientists use CV to judge consistency: in finance it compares the risk-per-unit-return of different investments, in manufacturing and quality control it flags whether a process is running consistently, and in laboratory science it reports assay or measurement precision. The tool takes a mean and a standard deviation you have already worked out (it does not read a raw data list), and the CV is shown as a percentage.

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Comments (1)

  • Editorial team

    This tool takes a mean and a standard deviation you have already worked out, so the choice between sample and population SD is yours. When you compare two datasets, use the same kind for both, or the difference in CV may come partly from that choice. Also check each mean is well away from zero, since a tiny mean inflates the CV. What are you comparing, such as two production lines, two assays or two investments?

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