Measure how spread out a set of numbers is. Enter your values separated by commas, spaces or new lines and the calculator returns both the population and sample standard deviation, along with the variance, the mean and the count. The difference matters: use the population version when your list is the entire group, and the sample version (which divides by n minus one) when your data is a sample drawn from a larger population. A larger standard deviation means the values are more scattered around the mean, while a small one means they cluster tightly. This is a core statistic for science, finance, quality control and grading. The math is exact and runs entirely in your browser, so your data stays private.