[header] How to calculate standard deviation [title] Look at your data set. [step] This is an important step in any type of statistical calculation, even if it is a simple figure like the mean or median. [substeps] Know how many numbers are in your sample. 
Do the numbers vary across a large range? Or are the differences between the numbers small, such as just a few decimal places? Know what type of data you are looking at. What do your numbers in your sample represent? This could be something like test scores, heart rate readings, height, weight etc.