Coefficient of Variation Calculator

CV% for one or more groups, with intra-assay and inter-assay summaries.

The coefficient of variation is the standard deviation divided by the mean, expressed as a percentage: CV% = (s / x̄) × 100. It lets you compare spread between measurements on different scales. In the lab, intra-assay CV is the average CV of replicates within one run, and inter-assay CV is the CV of the same control measured across runs.

Free, runs in your browser. Nothing you enter is uploaded.

Formula

CV% = (s / |x̄|) × 100,   s = √[Σ(x − x̄)² / (n − 1)]

The sample standard deviation (n − 1 denominator) is used, as in Excel's STDEV.S. The intra-assay figure is the mean of the per-sample CVs. The inter-assay figure is the CV of the group means, so enter one run or plate per line. CV is only meaningful for ratio-scale data with a true zero; it is undefined when the mean is zero and misleading for temperatures in °C or log-transformed values.

Questions

How do you calculate the coefficient of variation?

Divide the standard deviation by the mean and multiply by 100. For 98, 102, 101, 99 and 100 the mean is 100 and the SD is 1.58, so CV = 1.58%.

What is a good coefficient of variation?

It depends on the method. Many ELISA and immunoassay labs accept intra-assay CV under 10% and inter-assay CV under 15%. Bioanalytical guidelines allow up to 15%, or 20% at the lower limit of quantification.

What is the difference between intra-assay and inter-assay CV?

Intra-assay CV measures repeatability within one plate or run, from replicate wells of the same sample. Inter-assay CV measures reproducibility between runs, from the same control sample measured on different plates or days.

Should I use the sample or population standard deviation?

The sample SD (n − 1). Replicates are a sample of all possible measurements, and published CV acceptance limits assume the sample SD.

How do I calculate CV in Excel?

=STDEV.S(A1:A10)/AVERAGE(A1:A10), formatted as a percentage. The result matches this calculator.

References

More Statistics

All free tools · By Dr. Zubair Khalid, DVM, MS, PhD.