Standard Deviation Calculator
Find the mean, standard deviation and variance of any data set.
All calculations happen locally in your browser — nothing is uploaded, stored or tracked.
Add your data points
Use the row buttons to add as many values as you need.
Calculate
The statistics update immediately.
Read the summary
Mean, standard deviations, variance, min, max and range.
What Is Standard Deviation?
Standard deviation measures how spread out a set of numbers is. A small standard deviation means the values cluster close to the mean; a large one means they are spread widely. It is the square root of the variance and is expressed in the same units as the data.
The calculator reports both versions: the sample standard deviation (dividing by n − 1), used when your data is a sample of a larger population, and the population standard deviation (dividing by n), used when the data is the whole population.
The Formula
The mean is the sum of the values divided by the count. Each deviation is squared so positive and negative differences do not cancel out.
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Every calculation on this site runs in your browser using vanilla JavaScript. Nothing is uploaded, stored or tracked.
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- Works offline once loaded
Frequently Asked Questions
What is the difference between sample and population standard deviation?
Sample standard deviation divides by n − 1 to account for estimating from a sample; population divides by n and is used when you have every value.
How do I calculate standard deviation?
Find the mean, subtract it from each value, square the results, average them (n for population, n − 1 for sample), and take the square root.
What does a low standard deviation mean?
The values are close to the mean — the data is consistent. A high standard deviation means the values vary widely.
What is variance?
The standard deviation squared. It is in squared units, which is why standard deviation (in original units) is usually quoted.
Can I use this for exam scores?
Yes — enter the scores to see the class average and how much results vary around it.