Deluge downloaded file size variation

I use 'Transmission BitTorrent Client' for download bigger size from the very beginning of my linux use. But recently I read some post on famous linux related blog that there is an another powerfull BitTorrent client for Linux. It is 'Deluge'. So I am trying it from more then 3 weeks.Yes, Deluge has many kind of feature that I did not understand. I read Deluge FAQ file sevaral times. But failed to understand many of them. Actually I have less knowledge about torrent file or society.

Here is a variation I noticed and do not understand what is going there.

Look at the image above. I am downloaded "Ultimate Boot CD". I know that ISO file size is 301.4 MiB. But at the 'Stats' on bottom tab section it shows that file size is 432.2 MiB. What a huge difference.