A standard deviation calculator is a tool that computes the standard deviation of a given data set, which measures how spread out the values are from the mean. It can calculate either the population standard deviation or the sample standard deviation depending on if the data represents the whole population or just a sample. Key points about standard deviation:

• It is the square root of the variance.
• Population standard deviation divides by the total number of values.
• Sample standard deviation divides by the number of values minus one (to reduce bias).
• A low standard deviation means data points are close to the mean, while a high value indicates greater spread.

Several online calculators allow entering data separated by commas, spaces, or line breaks to instantly calculate standard deviation along with related statistics like mean, variance, and sum.