somthing like this will loop through a range, then stop and perform a
calculation when a non-blank cell is encountered.

Sub findFirstNonBlankCell()

Dim myRange As Range
Dim myVar As Range
Set myRange = Range("A2:A10")       'set range

'begin loop
For Each myVar In myRange
   Set nextVar = myVar.Offset(1, 0)

       If myVar = "" Then                 'test to see if cell is
empty
           Set myVar = nextVar         'proceed to next cell if empty
               Else                               'else perform a
calc.
           myVar.Value = myVar * 2  'peform a calucation
       End If
Next
End Sub

this will give you the row of the 1st blank cell in A

Option Explicit
Dim Blankrow As Long
Sub test()
Blankrow = Worksheets("Sheet1").Range("a1").End(xlDown).Row + 1
End Sub

range("A" & Blankrow) will give you the cell address