I need to populate a cell with the current file size of the active workbook.
I have tried:

Function FileSize(I As Integer)
FileSize = ThisWorkbook.BuiltinDocumentProperties(I)
End Function

and called the function in the sheet with:
=FileSize(22) ' 22 being the code for "Number of Bytes"
I get a #VALUE! error.

But if I use:
=FileSize(3) '3 being the code for "Author"
it works properly.

Any ideas?

Thanks,
Dave