I would say that portion size in general is a lot bigger in the US. One meal over there, I thought I would be safe in ordering a pastrami sandwich. In the end I took half of it out in a doggie bag and had it the following day. I had never seen so much meat!. Same with a piece of cheesecake, it was about twice what you would get in a restaurant here. That was NY and Dallas I was in.

However the one fast food place I went to - I found the portion to be about the same as the UK