A standard deviation is a statistical tool that tells you roughly how far, on average, each number in a list of data values varies from the average value or arithmetic mean of the list itself.
Instructions in this article apply to Excel 2019, 2016, 2013, 2010, 2007; Excel for Mac, Excel for Office 365, Excel Online, Excel for iPad, Excel for iPhone, and Excel for Android.
Practical Uses of the STDEV Function
In Excel, the STDEV function provides an estimate of a set of data's standard deviation. The function assumes that the entered numbers represent only a small portion or sample of the total population being studied. As a result, the STDEV function does not return the exact standard deviation. For example, for the numbers 1 and 2, the STDEV function in Excel returns an estimated value of 0.71 rather than the exact standard deviation of 0.5.
Even though the STDEV function only estimates a standard deviation, the function is useful when only a small part of a total population is being tested. For example, when testing manufactured products for conformity to the mean (for measures like size or durability) not every unit is tested and this forms an estimate of how much each unit in the entire population varies from the mean.
To show how close the results for STDEV are to the actual standard deviation (using the example above), the sample size used for the function was less than onethird of the total amount of data. The difference between the estimated and actual standard deviation is 0.02.
STDEV's Excel Syntax and Arguments
A function's syntax refers to the layout of the function and includes the function's name, brackets, comma separators, and arguments. The syntax for the Standard Deviation function is:
=STDEV(Number1,Number2,...Number255)
Number1 (required): This number can be actual numbers, a named range, or cell references to the location of data in a worksheet. If cell references are used, empty cells, Boolean values, text data, or error values in the range of cell references are ignored.
Number2, ... Number255 (optional): Up to 255 numbers can be entered.
Example of the STDEV Function
For this tutorial, the sample of data used for the function's Number argument is located in cells A5 to D7. The standard deviation for this data will be calculated. For comparison purposes, the standard deviation and the average for the complete data range A1 to D10 is included.
In Excel 2010 and Excel 2007, the formula must be entered manually.
Follow these steps to complete the task and calculate the information using the builtin function:
=STDEV(A5:D7)

Select cell D12 to make it the active cell. This is where the results for the STDEV function will display.

Type the function =STDEV(A5:D7) and press Enter.

The value in D12 changes to 2.37. This new value represents the estimated standard deviation of each number in the list from the average value of 4.5
For older versions of Excel, type the formula manually or select cell D12 and open the visual data selector via Formulas > More Functions > STDEV.