Kudos on understanding what he meant ade_ari, are you talking about the file size a user selects in an "upload file" form or the file size of an arbitrary file on their computer. The former can be done by uploading the file to your server's temp directory and using filesize()
yes u can use ajax to accomplish this.. call a php script which returns the filesize, and load the echoed result into a div
PHP can do this because it is server-side, but if you remember, Javascript is client-side and thus getting the file-size of a file on an external server would require communication to an external server. Thus as aforementioned, AJAX is the way to accomplish this.
As far as I understood, he wants to get the size of a local file. But something's telling me he won't come back anyway. =p