Standard Deviation
Free Standard Deviation: use =STDEV.S(range) for a sample, or =STDEV.P(range) when your data is the whole population.
n = 6 · mean = 14.67
Variance = 17.067
How it works
In Excel or Google Sheets, use =STDEV.S(range) for a sample, or =STDEV.P(range) when your data is the whole population.
Put your numbers in a single column or row.
In a blank cell type =STDEV.S( and select the range, then close the bracket.
Press Enter to get the sample standard deviation.
Use =STDEV.P(range) instead if your data covers the entire population, not a sample.
What this does
Standard deviation measures how spread out your numbers are around their average — small means tightly clustered, large means widely scattered. It is in the same units as the data, so a standard deviation of 4 on test scores literally means "give or take about 4 points". STDEV.S divides by n−1 for a sample; STDEV.P divides by n when you have every member of the group.
A worked example
For the values 12, 15, 9, 21, 17, 14, the mean is 14.67 and =STDEV.S(A1:A6) returns about 4.13. So a typical value sits roughly 4 units either side of the average. Variance — the square of that — is about 17.07. Paste your own list into the tool above and both update instantly. Standard deviation is the workhorse of any risk, quality or performance analysis — investment volatility, process control, test-score spread. The mean tells you the centre; standard deviation tells you how much to trust it.
Common mistakes
- Using STDEV.P on a sample (or STDEV.S on a full population), which biases the spread.
- Including text or blank cells in the range, which can skew or error the result.
- Comparing standard deviations of data measured in different units.
- Confusing standard deviation with the standard error of the mean — they answer different questions.
FAQ
STDEV.S or STDEV.P?
Use STDEV.S (sample, n−1) when your data is a sample drawn from a larger group — the usual case. Use STDEV.P (population, n) only when you have every single member.
What does a high standard deviation mean?
That values vary a lot around the mean — more risk or inconsistency. A low value means results are predictable and tightly grouped.
Is the old STDEV function still fine?
STDEV is the legacy name for STDEV.S and still works for backward compatibility, but new sheets should prefer the explicit STDEV.S / STDEV.P.
Related guides
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