The answer is 42

I guess about a year ago, the USPS set up several hundred R2-D2 skinned mail drop boxes. At the same time, but with much less fan fare, they released a .pdf for a paper version that you can sit on your desktop. Although I don't know how since I didn't even hear about the full sized versions until today.. At any rate, here's a view..

Photo courtsey of paperkraft on flickr

Well, here's the link to the .pdf to make your own:

http://www.starwars.com/kids/activity/crafts/f20070329/img/R2_D2PaperDoll.pdf

I might suggest using somehting heavier than regular copy paper if you want it to stand...