to give a user the size of his account (or the admin the size of the users folder)
in a more human readable format, you can use this PHP function.

it will scan the directory recursively and return the value in kilobytes, megabytes
so its easier to read.

download options for directories / human readable size

you can download the source as PHP file,

open the file as plain text in a new window or

get the code in a textarea to copy it.