I am doing a wedding cake shortly for a wedding that will have about 250 guests. I know not everyone will have cake so how many servings should I plan for?

Thanks!!

250.

For every person who doesn't eat cake, another person will eat two servings.

For ANY event, the host/hostess should order enough chairs, tables, plates, glasses, food and beverage for ALL the guests expectred to attend.

That said the invited # does not equal the expected #

this is something you need to discuss with your bride/customer.
Usually most decorators make a cake for the amount of people invited. Others downgrade that # by about 15-20%. Not many cakes will *perfectly* match the # of guests. Maybe what they pick out will only serve say 188; or another choise will serve 210. It's up to you as the professional/ decorator to point out to the bride these things while taking into consideration other aspects of the reception. Are they having an appitizer bar, and sit down dinner (like you see on those t.v shows) ? Then less people will eat cake. Is there an open bar? Drinkers don't eat sweets as much.
Who want to take the chance that they will run out of cake? People will bad-mouth the decorator for not making a big enough cake. Remind the bride that leftovers can be given to family, relatives, &/or friends and w/proper wrapping can be fzn.