Standard deviation measures how spread out numbers are around the mean. Sample standard deviation divides by n − 1 (use it for a sample from a larger group); population standard deviation divides by n.
How to calculate standard deviation
- Paste or type your numbers.
- Choose sample or population.
- Read the result and the working.
Formula
1. Find the mean. 2. Subtract the mean from each value and square the result. 3. Add the squares. 4. Divide by n − 1 (sample) or n (population) to get the variance. 5. Take the square root.
Frequently asked questions
Sample or population?
Use population only when you have every member of the group, such as all students in one class. Otherwise use sample.
Updated October 2026 · Built and tested by Sharjeel Tahir · How our tools are tested