Making a Cars tiered cake for a friend and I'm not sure how big to make. I've looked at both serving size charts but was hoping to get an opinion from someone else with more experience. She has invited 20 kids, expects most or all to show, each will at least bring one parent. Plus some family. So she says between 30-40 people, and she wants some cake leftover to take home. So... I can't decide between

a 12" round, 8" round, and 4" topper
or a 10"round, 8"round, and 4"topper

The one with the 12 in base will serve alot more needed , but I thik teh smaller one will not be big enough. Thoughts? Thanks for any help you can give.

it the topper, the 4 inch cake, being eaten?

wedding servings. the 12 and 8 gives 80, the 10 and 8 gives 62.
party servings. 12 and 8 gives 60, 10 and 8 gives 48.

so 10 and 8 inches is definatly plenty of servings, which ever way it gets cut. and the 4 inch will add on a few more if it gets counted. the sizing also makes a good cake - but maybe would look weird jumping down to the 4 inch? maybe better with a 6?

is this a gift, or are you getting paid for cost, or are you charging full price?
if you are giting, do whatever size you want, the actual cost diference isnt much. you want to do the bigger cake? why not! the bigger edge between the cakes gives you more to work with.

if you are getting paid for cost, then you will need to clear it with the friend.
charging full price as a business, then you want the right number of servings (unless she is happy to pay the extra), ie, as close to 40 as possible.

some things to think about, but the smaller sizes will totally serve the guests.
xx

that's some good advice she ^^^ gave you
Personally I prefer the 12,8 (or9), 4 option. To me it looks better and as was pointed out there is more ledge room to work with. Also delivery is much less worrisome - whether you deliver or they p/u.