Standard Deviation Calculator

This calculator measures how spread out a list of numbers is around its average, a summary statistic used across maths, science, quality control and business reporting. A small standard deviation means your data points sit close to the mean, while a large one signals wide variation, handy when comparing test scores, production measurements, survey results or investment returns. You type or paste your numbers into the box, separated by commas, spaces or new lines, and results update instantly as you type. It returns the sample standard deviation as the main result, plus the population standard deviation, the sample variance, the mean, and a count of your values. The two standard deviations differ because the sample version divides by one less than the count, correcting for a small sample understating the true spread of the wider population it comes from. Use the population figure when your list is the entire group you care about, such as every student in one class, and use the sample figure when your numbers are drawn from a bigger group you are estimating, such as a survey of some customers. Because results recalculate live, you can test how adding, removing or correcting a number changes the spread, useful for checking data before you report or analyse it further.

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