Row count where data exists

Assuming that your Sheet1 is not necessary active you would need to use this improved code of yours:

i = ActiveWorkbook.Worksheets("Sheet1").Range("A2" , Worksheets("Sheet1").Range("A2").End(xlDown)).Rows.Count

Look into full worksheet reference for second argument for Range(arg1, arg2) which important in this situation.

If you need VBA, you could do something quick like this:

Sub Test()
    With ActiveSheet
    lastRow = .Cells(.Rows.Count, "A").End(xlUp).Row
    MsgBox lastRow
    End With
End Sub

This will print the number of the last row with data in it. Obviously don't need MsgBox in there if you're using it for some other purpose, but lastRow will become that value nonetheless.