PERCENTRANK function
Returns the rank of a value in a data set as a percentage of the data set. This function can be used to evaluate the relative standing of a value within a data set. For example, you can use PERCENTRANK to evaluate the standing of an aptitude test score among all scores for the test.
Syntax
PERCENTRANK(array,x,significance)
Array is the array or range of data with numeric values that defines relative standing.
X is the value for which you want to know the rank.
Significance is an optional value that identifies the number of significant digits for the returned percentage value. If omitted, PERCENTRANK uses three digits (0.xxx).
Remarks

If array is empty, PERCENTRANK returns the #NUM! error value.

If significance < 1, PERCENTRANK returns the #NUM! error value.

If x does not match one of the values in array, PERCENTRANK interpolates to return the correct percentage rank.
Example
The example may be easier to understand if you copy it to a blank worksheet.
How to copy an example

Create a blank workbook or worksheet.

Select the example in the Help topic.
Note Do not select the row or column headers.
Selecting an example from Help

Press CTRL+C.

In the worksheet, select cell A1, and press CTRL+V.

To switch between viewing the results and viewing the formulas that return the results, press CTRL+` (grave accent), or on the Formulas tab, in the Formula Auditing group, click the Show Formulas button.
A 

Data 

13 

12 

11 

8 

4 

3 

2 

1 

1 

1 

Formula 
Description (Result) 
=PERCENTRANK(A2:A11,2) 
Percent rank of 2 in the list above (0.333, because 3 values in the set are smaller than 2, and 6 are larger than 2; 3/(3+6)=0.333) 
=PERCENTRANK(A2:A11,4) 
Percent rank of 4 in the list above (0.555) 
=PERCENTRANK(A2:A11,8) 
Percent rank of 8 in the list above (0.666) 
=PERCENTRANK(A2:A11,5) 
Percent rank of 5 in the list above (0.583, onequarter of the way between the PERCENTRANK of 4 and the PERCENTRANK of 8) 
Note To view the number as a percentage, select the cell, and then on the Sheet tab, in the Number group, click Percent Style .