Free Standard Deviation Calculator
Calculate mean, variance and standard deviation.
What is the Standard Deviation Calculator?
An average alone hides a lot — two data sets can share the same mean while one is tightly clustered and the other wildly spread out. Standard deviation measures that spread, telling you how far values typically sit from the average.
This calculator finds the mean, variance and standard deviation of a data set, giving both the population and sample versions, right in your browser.
Last updated: Aug 12, 2026
What does this tool do?
You paste a list of numbers and the tool computes the mean, then how far the values deviate from it on average.
It reports both population standard deviation (when your data is the whole group) and sample standard deviation (when it's a subset), since the two use slightly different formulas.
Key features
Population and sample
Both standard deviations, side by side.
Mean and variance
The full set of spread statistics.
Flexible input
Commas, spaces or new lines all work.
Instant
Results update as you edit the data.
Private
Your numbers are calculated in the browser.
Example
Common use cases
- Students — Solve statistics coursework.
- Researchers — Summarize the spread of results.
- Analysts — Measure variability in data.
- Teachers — Check statistics answers.
- Quality engineers — Track process consistency.
- Investors — Gauge the volatility of returns.
- Scientists — Report measurement uncertainty.
- Sports analysts — Compare consistency across players.
Benefits
- It shows spread, which the mean alone can't.
- It gives both population and sample versions.
- It handles messy pasted data.
- Your numbers stay on your device.
Tips
- Use sample standard deviation when your data is a subset of a larger group.
- Use population standard deviation when you have the entire group.
- A larger standard deviation means more spread-out data.
- Standard deviation is in the same units as your data; variance is squared.
- Outliers inflate standard deviation, so check for them.
- About two-thirds of normally distributed data falls within one standard deviation of the mean.
- Separate values with commas, spaces or new lines.
- Pair it with the average calculator for the full picture.
Common mistakes to avoid
Using population when you have a sample
Fix: For a subset of a larger group, use the sample standard deviation.
Comparing variance to raw data
Fix: Variance is in squared units — use standard deviation to compare with the data itself.
Ignoring outliers
Fix: A single extreme value can inflate the spread; check the data first.
Too few data points
Fix: Sample standard deviation needs at least two values.
How it works
- 1
Enter data
Paste your numbers.
- 2
See the spread
Mean, variance and deviation appear instantly.
Frequently asked questions
It shows both — use sample when your data is a subset, and population when it's the whole group.
Separate values with commas, spaces or new lines.
It shows both — use sample when your data is a subset, and population when it's the whole group.
Separate values with commas, spaces or new lines.
Standard deviation is the square root of variance, so it's in the same units as your data and easier to interpret.
The values are more spread out from the mean; a small one means they're tightly clustered.
Yes. Extreme values increase the standard deviation, so review your data for them.
No. Everything is calculated in your browser.
Conclusion
Standard deviation turns an average into a fuller story about your data's spread. Pair it with the average calculator to summarize any data set.