I have a request for a cake for about 40 people. Do you thing a 10 inch square 2 layer cake with a 8 inch round 2 layer on top with a 6 inch ball on top will be enough?

That will give you approximately 84 servings, so yes, you will have more than enough!

Just the 10" square will give you 50 servings.

If you want a tiered look, the 6" and 8" rounds will give you 36 servings. Or you can do a 10" round for 38 servings.

Hope that helps

Here's a servings guideline that a fellow CC member made. Hope it helps!
http://shinymetalobjects.net/cake/calculator/cake_calculator.cgi

Thanks, sorry about the misspelled....suppose to be think not thing.
I was going to do a tuxedo cake with a ball and chain on top for a grooms cake....thanks

an 8" square and 6" round will give you 40 servings

www.wilton.com has the servings chart. It's the one you want to use.

I'm doing a 10" square this weekend for 38 people, it's suppose to serve 50. Why is it that a 10" square and a 10" round use the same amount of batter but the serving count is so much higher with the square? Is there that much that they allow/discard for for cutting the round?

I use much more batter for a square cake than I do a round cake