How in the world do you figure out the number of servings and the cake size to start off with? Do you go up to the next size cake

I'm not worried about pricing as I have that figured out. I typically don't do many 3d cakes so I have a hard time trying to figure out how to construct it and estimate servings. For example I received an inquiry about doing a pillow cake (I have done one before, but that was way back before the business when I made one for a family party. I had no idea how many it served.) anyways....the potential client would like for it to serve 30 or possibly fewer as she may supplement with matching cupcakes. I know how many servings a typical square cake is to feed, I have no idea about how many servings i'm going to have once I carved it down.

For example if I start with an 8" square (serving 32) would I end up with about 20-25 servings? How much would a 10" square serve after carving it down to a square pillow shape?

I need a closer way of figuring this out. Is there a percentage I should go by? Cause if so that will make the stress of designing these cakes go down.

TIA

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

Wilton has some pillow shaped pans, and on the above chart they have a size of the pan and servings, so for a pillow I'd use those numbers as a base to go off of.

Thank you Texas. I actually have the instructions for those pans open in another tab. I don't have a 7" or 13" square so those didn't help. I got that the 10" will go down to about 40 servings. I'm still lost on what to do in general for anything else.

I think I just don't get it. I'm frustrated and thinking i'm just not going to do carved cakes. This stresses me out every time someone ask for a 3d cake.

To make sure they have enough cake I just kind of wing it.
I picture the cake in my head after it would be carved and picture how I would cut it then just count how many it would feed.
With this particular cake I think because there would be cupcakes you would be fine with what ever size.
I think if you had an official mathmatical method you will have more room for error than just going by each and every carved cake and using your head to figure it out.
Another way to make this easier is laying all of your cake pans down to see how big the cake will roughly be once it's carved. Then it's easier to see how much actual cake will be there.

I tend to start with shapes that are similar to what I am going for. Like the cow cake in my photos, I used oval pans and the mine wonder molds. That way I don't have to trim off too much, and still have a basic idea to go from.

So I think it will all depend on what shape you need, what shapes you bake, and how much you have to take off. I'm not sure there is a percentage amount that you can go off of since it can very. If anything, I'd give them a range of serving.