The Skew of a population is a measurement of the asymmetry of the distribution about the mean.
Positive Skew  Negative Skew 
The Excel SKEW.P function calculates the skewness of the distribution of a supplied set of values.
Note: the Skew.P function was only introduced in Excel 2013 and so is not available in earlier versions of Excel.
The format of the function is:
Where the number arguments provide a minimum of 3 values that make up the data set. These can be individual numbers or arrays of numbers.
A  B  

1  1  
2  1  
3  2  
4  2  
5  2  
6  2  
7  3  
8  3  
9  3  
10  4  
11  4  
12  5  
13  6  
14  7  
15  8 
Column A of the above spreadsheet on the right shows 15 data values. The distribution of these values is shown in the chart below:
The population skewness of the values in the spreadsheet can be calculated using the Excel Skew.P Function as follows:
This gives the result 0.774523929, which indicates that the data set has a positive skew.
Further details and examples of the Excel Skew.P function are provided on the Microsoft Office website.
If you get an error from the Excel Skew.P function this is likely to be one of the following:
#DIV/0!    Occurs if either:

#VALUE!    Occurs if any of the supplied number arguments that are supplied directly to the function are not recognised as numeric values. (Note that if the Skew.P function is provided with a reference to a range of cells, any text values within this cell range are simply ignored and do not cause the function to return an error). 