Cake pan boxes list a diameter, not a guest count, which is why party planners and home bakers alike end up guessing — and often over- or under-baking. Professional bakeries solve this with published serving charts that account for how a cake is actually cut, not just its raw surface area.
Why servings aren't just pan area ÷ slice area
A quick area calculation — pan area divided by slice area — gets you in the right neighborhood, but it overstates real yields, especially for round pans. Round cakes lose usable cutting area near the curved edge (a rectangular slice grid never perfectly tiles a circle), and very small pans have a practical minimum slice count regardless of the math. This calculator uses Wilton's published serving chart, which is based on how bakeries actually cut cakes for a standard 4-inch-tall, two-layer cake, rather than a theoretical area formula.
Party cut vs. wedding cut
The single biggest lever on serving count is slice size, not pan size. A party-cut slice (about 1½ × 2 in) is a full dessert portion for a casual gathering. A wedding-cut slice (about 1 × 2 in) is smaller, sized for a formal event where cake is one of several desserts on the table. The same 9-in round pan serves 24 at party size but 32 at wedding size — a 33% swing from slice size alone.
Tiered and multi-pan cakes
For a tiered cake, don't try to combine tiers into one pan lookup — run each tier's pan size through the calculator separately and add the results together. Cake height matters too: the chart assumes a standard 4-inch-tall, two-layer cake. A 3-to-6-inch cake in the same pan yields about the same count, but a single, un-layered cake shorter than 3 inches will only yield roughly half as many servings.