How to Calculate Relative Standard Deviation in Excel
For sample data in A2:A11, enter =STDEV.S(A2:A11)/ABS(AVERAGE(A2:A11)), then format the result as a percentage. Use STDEV.P instead when the range is the entire population.
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The formula returns a decimal ratio. Apply Excel’s Percentage format; do not also multiply by 100.
Generate and check your Excel RSD formula
Paste data to verify the mean, standard deviation, and relative standard deviation before using the generated formula in Excel.
Calculate RSD in Excel step by step
- Place numeric observations in one column, for example A2:A11.
- For a sample, calculate standard deviation with =STDEV.S(A2:A11).
- Calculate the mean with =AVERAGE(A2:A11).
- Divide the SD by the magnitude of the mean: =STDEV.S(A2:A11)/ABS(AVERAGE(A2:A11)).
- Choose Percentage format and set the desired decimal places.
Using ABS keeps RSD non-negative if a data set has a negative mean. If your field defines a signed coefficient of variation, follow that field’s convention instead.
Should you use STDEV.S or STDEV.P?
| Your range represents | Excel function | Divisor |
|---|---|---|
| A sample from a larger population | STDEV.S | n − 1 |
| The complete population of interest | STDEV.P | n |
Microsoft specifies STDEV.S for sample data and STDEV.P for the entire population. The difference becomes small for large data sets but should still be chosen from the study design, not from whichever result looks better.
How to calculate mean and standard deviation in Excel
Use =AVERAGE(range) for the arithmetic mean. Use =STDEV.S(range) or =STDEV.P(range) for standard deviation. RSD—also called the coefficient of variation in many contexts—then expresses standard deviation relative to the mean, which makes spread easier to compare across scales.
Common Excel RSD mistakes
- Multiplying by 100 and using Percentage format: that scales the display twice. Either use the ratio formula and Percentage format, or multiply by 100 and leave the cell as a regular number.
- Mean equals zero: RSD is undefined because division by zero is impossible.
- Mixing units: all observations must measure the same quantity in the same unit.
- Using STDEV.P for sampled measurements: choose STDEV.S unless your range is the entire population of interest.
Frequently asked questions
What is the Excel formula for RSD?
For sample values in A2:A11, use =STDEV.S(A2:A11)/ABS(AVERAGE(A2:A11)) and format the cell as a percentage.
Is RSD the same as standard deviation?
No. Standard deviation uses the data’s unit. RSD divides that SD by the magnitude of the mean and is usually shown as a percentage.
Can I calculate RSD when the mean is zero?
No. The denominator is zero, so the ratio is undefined and should not be reported as 0%.
Does Excel ignore blank cells?
STDEV.S, STDEV.P, and AVERAGE ignore empty cells and text in references, but error values can propagate errors.
Related calculators and official references
Use the coefficient of variation calculator for raw or summary data, the pooled standard deviation calculator to combine group SDs, or the grouped-data standard deviation calculator for a frequency table.