FileLen Function:

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

Syntax:
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
	Else
		FileLen = CLng( objFile.Size )
	End If
	Set objFile	= Nothing
	Set objFSO	= Nothing
	On Error GoTo 0
End Function
%>