EXCEL VBA - how many rows data we are going to handle in loop?

Range("a" & Rows.Count).End(xlUp).Row


MsgBox (Range("a" & Rows.Count).End(xlUp).Row)
          ' from bottom to the last filled cell

     
With Cells :
 

MsgBox (Cells(Sheets("Sheet1").Rows.Count, "A").End(xlUp).Row)