Standard Deviation Calculator
Calculate sample or population standard deviation, variance, and mean from your numbers, with results that update as you type.
Use when your data represents a subset of a larger population. Applies Bessel's correction.
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Input your numbers into the Standard Deviation Calculator panel to see real-time statistics, variance, and normal distribution charts.
Sample & Population
SD modes
Live Results
As you type
Mean & Variance
Summary statistics
In Your Browser
Local calculations
Free
Free
What is Standard Deviation?
Standard deviation measures how spread out numbers are from their average (mean). A low standard deviation means data points are close to the mean; a high standard deviation means they're spread over a wide range.
For example, test scores with a mean of 75 and an SD of 5 have a one-SD interval from 70 to 80. An SD of 15 widens that interval to 60–90. How many scores fall in that interval depends on the distribution.
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Common Questions
What if my standard deviation is zero?
All your values are identical—there's no variation in the data.
Which mode should I use?
Use Sample (n-1) for subsets, Population (N) for complete datasets.
How accurate is this calculator?
Calculations use JavaScript double-precision numbers. Results are rounded for display; very large or very small values can exceed the supported numeric range.
Is my data stored?
No. All calculations happen locally in your browser.
What's the difference from variance?
Standard deviation is the square root of variance, in the same units as your data.
Ready to Analyze Your Data?
Enter your numbers and choose sample or population mode. Free to use, with no signup required.
Start Calculating