FileLen Function:

The FileLen function returns a long representing the size of a file in bytes. If file is not found, FileLen returns Null.

long = FileLen(pathname)
Example Usage:
<% = FileLen( server.mappath("/New Folder/file.asp") ) %>
ASP Source Code:
Private Function FileLen(byVal pathname)
	Dim objFSO, objFile
	On Error Resume Next
	Set objFSO	= Server.CreateObject("Scripting.FileSystemObject")
	Set objFile	= objFSO.GetFile(pathname)
	If Err Then
		FileLen = Null
		FileLen = CLng( objFile.Size )
	End If
	Set objFile	= Nothing
	Set objFSO	= Nothing
	On Error GoTo 0
End Function