How Much Cake Do I Need for a Party?
Start with required servings, not cake diameter. Cake shape, height and cutting style all change how many portions a cake produces.
Step 1: estimate cake take-up
Not every guest necessarily eats cake, especially when other desserts are available. Choose an expected percentage rather than assuming either 0% or 100% without thinking about the menu.
Step 2: decide whether you want extra servings
Add a deliberate contingency if you want generous cutting, seconds or leftovers. Keep that separate from the expected guest demand.
Step 3: match servings to the actual cake
Use the baker, recipe or manufacturer’s portion information for the cake’s shape, height and cutting pattern. That is more defensible than claiming a particular diameter always serves the same number.
Example
Thirty guests at 90% expected take-up gives 27 servings. A 10% contingency brings the target to 29.7, so you would choose a cake or combination of cakes providing at least 30 suitable portions.
Use the Cake Serving Calculator to build your own target.