Using a variable in a VB Excel macro

I am writing a VB macro in Microsoft Excel which automatically creates a pivot table from two tabs within the spreadsheet.  This macro will be used multiple times, each time with a different amount of data in it, in turn, I need to make the macro dynamic so that it will read in more or less data each time.    I have written a loop to find the last row in my spreadsheet and saved that number as a variable (r or f)  I want to use that variable in range type lines of code, but don't think I am doing it correctly.  

For example, currently, I have
RANGE("F2:F10896").select

However, the next time this is run there will be more than 10896 records, so I need that to be dynamic.  I can't imagine that I can use the following code:

RANGE("F2:FT").select

This is extremely important, so I can assure you an A and max points.