About this tool
The Pizza Party Calculator is a free, in-browser tool that tells you how many pizzas to order for a crowd. It uses the caterer's 3/8 rule — about 3 slices per adult from an 8-slice pie — and adjusts for appetite, pizza size, kids, and the number of topping varieties you want. Enter your headcount and it returns pizzas to order, total slices, per-variety split, leftover slices, and total cost if you add a price. Everything is calculated locally in your browser.
Slices per pizza depend on diameter: a small 10-inch has 6 slices, a medium 12-inch has 8, a large 14-inch has 10, and an extra-large 16-inch has 12. Appetite sets slices per guest — light 2, average 3, hungry 4 — and kids are counted as half an adult. Total slices = (adults + 0.5 × kids) × slices per guest, and pizzas = ceil(total slices ÷ slices per pizza). If you want several varieties, the count is split evenly and each variety is rounded up, so you may end up ordering a couple of extra slices' worth to keep at least one pizza of each kind. Leftovers = pizzas × slices per pizza − total slices.
As a worked example, 20 adults with an average appetite eating large 14-inch pizzas (10 slices) need 20 × 3 = 60 slices, so ceil(60 ÷ 10) = 6 pizzas, with no leftovers. Bump appetite to hungry (4 slices) and it becomes 80 slices, or 8 large pizzas. When guests span a wide range, order to the hungrier end — a few leftover slices are cheaper than running short.