Standard Deviation Calculator
Paste a list of numbers to get the mean, variance, and sample and population standard deviation in one place.
Your data
Statistics
Sample standard deviation
Standard deviation tells you how much your data varies
An average on its own can mislead. A 5% conversion rate sounds great until you see a standard deviation of 3 points, which means some weeks you hit 8% and others 2%. Metrics with high variance need bigger samples before you can draw solid conclusions, and standard deviation is how you measure that variance.
How to read the results
- Mean: the average of your numbers.
- Variance: the average squared distance from the mean.
- Standard deviation: the square root of the variance, in the same units as your data.
- Coefficient of variation: standard deviation divided by the mean, useful for comparing spread across metrics of different sizes.
In a roughly normal distribution, about 68% of values fall within one standard deviation of the mean and about 95% fall within two.
Frequently asked questions
Should I use sample or population?
Use the sample formula (n - 1) when your data is a sample of a larger group, which covers analytics, surveys and most marketing data. Use the population formula only when you have every value in the group.
Why is the sample result larger?
Dividing by n - 1 instead of n corrects for the fact that a sample tends to underestimate the true spread. The difference shrinks as your data set grows.