Party Calculators
Party pizza quantity.
Enter adults, children and slices each will eat. See how many pizzas to order, how many to make vegetarian, leftover slices, cost and the pizza area behind each slice. Runs in your browser; nothing is sent or stored.
Your party
Result
Fill the form and press Calculate.
Party Pizza Quantity Calculator: the short answer
Plan about 3 slices per adult and 2 per child, add a 10% buffer, and divide by the slices per pizza. For 12 adults and 8 children that is 8 pizzas of 8 slices.
Worked example
12 adults at 3 slices and 8 children at 2 slices need 12 x 3 + 8 x 2 = 52 slices. Add a 10% buffer: 52 x 1.1 = 57.2 slices. At 8 slices per pizza, 57.2 / 8 = 7.15, rounded up to 8 pizzas (12 slices left over). With 25% vegetarian, 2 of the 8 are vegetarian and 6 regular. At $18 each the cost is $144.00, or $7.20 per guest. A 14 inch pizza has an area of pi x 14 x 14 / 4 = 153.9 square inches, so each of 8 slices is 19.2 square inches.
How it works
Slices needed = adults x slices per adult + children x slices per child. Pizzas = round up (slices needed x (1 + extra) / slices per pizza), at least 1. Vegetarian pizzas = the share you choose, rounded, but at least one when the share is above zero. Pizza area = pi x diameter squared / 4.
Slices per person are rules of thumb, not a published standard. Hungry teens, a long event or no other food push the number up; a buffet with many other dishes pushes it down.
Sources and basis (opened 2026-10-08): Arithmetic and circle geometry on the numbers you enter. The 3 slices per adult, 2 per child and 10% extra are planning defaults, not sourced figures.
FAQ
How many pizzas per person?
A common rule of thumb is about 3 slices per adult and 2 per child, which is roughly 1 large pizza for every 2 to 3 adults. It varies by appetite and by what else is served.
How many pizzas for 20 people?
For 12 adults and 8 children at 3 and 2 slices, with 8 slices per pizza and a 10% buffer, the calculator gives 8 pizzas.
How many vegetarian pizzas should I order?
Set the share to match your guests. Any share above zero gives at least one vegetarian pizza.
Why does pizza size matter?
It does not change the pizza count, which depends on slices per pizza. It shows the area per slice so you can compare a 12 inch with a 16 inch pizza.
Does this include sides?
No. If you serve wings, salad or dessert, lower the slices per person.