When I do cupcake cakes, I use the half sheet cakeboard (got them at Michaels - I think they are Wilton) and usually 24 cupcakes make a good CCC. I would think you can get about 30 on a 1/2 and a full would definitely hold 48 standard sized cupcakes.
Cakediva73 is absolutely right! I can usually get about 30-36 on a half sheet...recently I did a cars cupcake cake (see photos) that had 48...I used a full sheet cake board and had plenty of room along the outside to include a few extra cupcakes.
Vita brevis, ars longa. (Life is short, art forever.)