4 - 5lbs. It also depends on how many adults and kids you have. My son just had his birthday party for about 45 people (29 adults & 16 kids). I've ordered a 5lbs cake. We can't even finish all.
It depends whether you would provide other food and how much. And what time is your party (if it's in the afternoon say 2 or 3pm after lunch, people might not be very hungry)
I just had a party for my son for around 24 kids and 30 adults. We just had a 3lb cake as we have many other foods to provide (sausages, sphaghetti, fish balls, tulip cake, chicken wings, potato chips, candies, etc). We had a lot of food left and the cake was just finished.
The party will be at McDonald's. People can order food freely. Party time will be from 11:30 - 13:00. We'll have 50-55 people to join the party. Will a 5 lbs cake be enough?
You're right. I have already checked with McDonald's, based on their experiences, 4 lbs cake would be more than enough! They had a party for 50 people last week & could only finished half of the 4 lbs cake.