Can you explain a bit further if you mean for the editor or somebody else and how you see it work? It's quite easy to read the size of MediaData if you wan't to show it somewhere. You could for example append it to the name showing in the media gadget when file is updated/added. I recall doing something like URLifying and having it like: the-name-400kb.jpg. It's also quite easy to iterate A-elements and burn the file size and file type in to the link text for example in the creating/saving event, something like "Download the file (JPG file, 2 MB)".