Relative Standard Deviation Calculator
Express variability as a percentage of the mean — the relative standard deviation (RSD), also called the coefficient of variation, from your mean and SD.
How it works
RSD = (standard deviation ÷ |mean|) × 100%
The relative standard deviation, or coefficient of variation expressed as a percentage, rescales spread relative to the average so you can compare variability across data sets with different units or magnitudes. A wage set with an RSD of 8% is far more consistent than one at 40%, regardless of the currency. It is widely used in analytical chemistry and quality control to judge measurement precision, and only makes sense for ratio data with a meaningful, non-zero mean.
Worked example
A set of measurements has a mean of 80 and a standard deviation of 12. The RSD is (12 ÷ 80) × 100% = 15%, meaning typical values deviate from the average by about 15%.
Sources: Coefficient of variation — Wikipedia
Frequently asked questions
How is RSD different from the coefficient of variation?
They are the same quantity — RSD is simply the coefficient of variation written as a percentage. The coefficient of variation is often quoted as a plain ratio (0.15), while RSD is 15%.
What is considered a good RSD?
It depends on the field. In analytical labs an RSD under a few percent signals precise measurement, while in biology or finance much larger values are normal. As a loose guide, under 10% is very consistent and over 30% is highly variable.
Why can I not use RSD when the mean is zero or negative?
Dividing by a mean of zero is undefined, and a mean that straddles zero makes the ratio meaningless. RSD is intended for positive ratio-scale data such as concentrations, prices or weights.
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