Standard deviation measures how spread out your numbers are around the mean: you find the mean, average the squared differences from it to get the variance, then take the square root. The browser-based standard deviation calculator gives both the population and sample standard deviation from a pasted list, with nothing uploaded.
Standard deviation tells you the typical distance of a value from the mean. The steps are: calculate the mean, subtract it from each value and square the result, average those squared differences to get the variance, then take the square root of the variance. A small standard deviation means the numbers cluster close to the mean, while a large one means they are widely scattered.
There are two versions. The population standard deviation divides the summed squared differences by the count of values, and is used when your data covers the entire group. The sample standard deviation divides by the count minus one, and is used when your data is a sample drawn from a larger group. The calculator reports both so you can pick the correct one, and it does the arithmetic in your browser.
The population version divides by the number of values, while the sample version divides by that number minus one. Use the sample version when your data is a sample of a larger group.
Yes. The variance is the square of the standard deviation and is reported alongside it.
Yes. The whole calculation runs in your browser with nothing sent to a server.