Pastry Girl~~Here is some information that should be very helpful for you:
Nearly ALL custom bakeries in the USA use the Wilton Wedding serving chart to determine the pricing per serving. Individual custom bakers may choose whatever they want to use to price their cakes. Keep in mind that NOBODY out there in the general public has any idea how to get 24 wedding cake slices out of an 8" round, 4" high cake tier. (Be aware that even though the charts indicate 24 servings slices can be had from an 8" x 4" high round tier, that most people will only get about 10-12 servings from and 8x4" cake.) Most wedding cakes are cut and served by a professional caterer or staff person at the venue.
The assumption with wedding cakes is that there will be other food served at the event, and the cake will be a symbolic, small slice.
Party (or Earlene) slices are generally used when there is no other food at the party/celebration.
Wedding: 1 wide x 2 in. deep x 4" high slice
Party: 1.5 wide x 2 in deep x 4" high slice
Earlene's Serving Chart (for slightly larger slices, probably 2x2x4"):
It is up to YOU, the professional custom baker, to educate the client about HOW to cut the cake to get 24 wedding-sized slices out of an 8x4" cake.
Here's a couple of very helpful links:
"how to cut a wedding cake:
Sample Cake Serving Sizes -- made of Paper or Cardstock
Here are two wonderful links that show you drawings of different cake configurations and also photos of actual cakes configured for different amounts of total servings: