Estimates standard deviation based on a sample. The standard deviation is a measure of how widely values are dispersed from the average value (the mean).
Syntax
STDEV(number1,number2,...)
Number1,number2,... are 1 to 30 number arguments corresponding to a sample of a population.
Remarks

Logical values such as TRUE and FALSE and text are ignored. If logical values and text must not be ignored, use the STDEVA function.

STDEV assumes that its arguments are a sample of the population. If your data represents the entire population, then compute the standard deviation using STDEVP.

The standard deviation is calculated using the "nonbiased" or "n1" method.

STDEV uses the following formula:
Example
Suppose 10 tools stamped from the same machine during a production run are collected as a random sample and measured for breaking strength.
St1 
St2 
St3 
St4 
St5 
St6 
St7 
St8 
St9 
St10 
Formula 
Description (Result) 
1345 
1301 
1368 
1322 
1310 
1370 
1318 
1350 
1303 
1299 
=STDEV([St1], [St2], [St3], [St4], [St5], [St6], [St7], [St8], [St9], [St10]) 
Standard deviation of breaking strength (27.46391572) 