Find cake size for your guest count.
Cake servings come from surface area divided by portion area, which is why sizes scale much faster than the diameter suggests: a 12 inch round cake has 113 square inches against a 10 inch cake's 79, so it yields 44% more slices for two inches more width. Portion convention matters as much as size. A wedding portion is a 1 by 2 inch finger, four square inches, while a party slice at 2 by 2 is double that and a generous dessert portion triple. Stacking layers does not add servings — it makes each slice taller — so a tiered cake is counted tier by tier, adding the servings from each.
Cake Serving Size
Area = pi x (diameter/2)^2 for round or side^2 for square; servings = area / portion area; size needed = sqrt(guests x portion area / pi) x 2 for round
About 28 wedding portions or 14 party slices from a single tier. A 12 inch round has 113 square inches of surface, divided by the portion size you are cutting.
No. Layers stacked vertically make each slice taller. To serve more people you need more surface area — a wider cake or additional tiers, counted separately.