12 inch round cake 4inches high? 10 inch round 4 inches hight? 8 inch round 4 inches high? I have a cake chart but it's confusing and what it tells me for each seems like way too much. I need enough cake for 30 people and I have prepared a cake of each size mentioned above but I don't want to have to use all of them unless necessary. TIA.

The 8" serves 24; the 10" serves 38 and the 12" serves 56.

http://www.wilton.com/cakes/making-cakes/baking-wedding-cake-2-inch-pans.cfm

Surface area of a 1"x2" slice of cake is 2.

Surface area of a round cake is radius squared times pie.
The radius = 1/2 of the diameter, which is the size of the round.
Pie = 3.14
To square a number means to multiply it by itself

So, for the 8" round cake, the surface area is (4x4)x3.14 = 16x3.14 = 50.24

Divide the surface area of the cake by the surface area of the slice

50.24 divided by 2 = 25.12
So, an 8" round cake gives 25 servings. I *think* the charts say 24 just to be on the safe side.

I always use Earlene...

http://www.earlenescakes.com/ckserchart.htm

Her serving sizes are a bit bigger than Wilton, both guides are great!

Why do you need more than 8 cubic inches of cake in a serving? You don't. If they want to cut bigger pieces, then they can order more cake. I'm not going to give them larger pieces, which is basically giving cake away for free, which is what following the Earlene chart does, unless you charge more per serving to compensate.

Earlene is a giant in cake decorating, and is to be given the utmost respect for advance the cake arts, but her serving charts do a great disservice .

Thanks to all for your help. I'm very grateful!

[quote="KHalstead]
i always figured out the slice i wanted 1" x 2" x 4" = 8 cubic inches.

then take your cake, we'll take an 8" cake for instance
take the length x width x height (for round cakes use 1" less for height to account for the lost corners)

8" x 8" x 3"'=192 divide that by the cubic inches of your slice (8")
192 divided by 8=24

if it's a square cake use the full 4" height.

this way if you wanted to serve a bigger slice of cake, it's easy to figure out servings too........such as a 1"x3"x4" slice would be 12 cubic inches

192 divided by 12 =16 servings for an 8" round[/quote]

You're right that the volume of a serving is 8 cubic inches, but why go through the extra step to figure out the volume of cakes when all you need is the surface area?

Even in your jumbo slice example, surface area suffices. Divide the surface area of 50.24 by 3 (which is the surface area of the 1x3x4 slice), and you get 16.7466...so 16 servings.

The correct way to find the volume of a cylinder is multiply the surface area by the height: (r x r) x pi x h
For an 8"x4" round cake that comes out to 200.96
Divide that by 8 and you get 25.12
So, the cake will yield 25 servings. You've been shorting yourself a serving.

been shorting more than that because I consider it to be 20 servings lol

I always round down to the closest 5 in case I stay to cut the cake, so I have a buffer zone for my servings (I better get out of it what I said it could yield)

by the way, how do you get the surface area?

radius is 4 on a 8" cake right?

So 4x4xpix4? ok, I got it!