I'd get a full sheet cake. I always like to have plenty. If there's any left over, send it home with your guests.
http://www.hurryupcakes.com/general-cake...
18-40 depending on the slice size. I'd think you are fine
I am hosting a baby shower and I would really like to do a half sheet cake instead of cupcakes. Right now we have 19 adults who have RSVP and 5 kids. We invited around 40 people but are expecting around 30 or so to show up. Do you think a double layer half sheet cake will feed enough people? I would hate to be in an awkward situation and not have enough cakes, but I think a full sheet will be way to big, not to mention very expensive and unnecessarily. What is your experience with a half sheet cakes, do you think it will feed enough people?
I looked up on like and it says between 18 and 40 people. that is a big variation. I believe most on the guess will be women.