The 3/8 rule for ordering pizza

The rule

Multiply the number of guests by 3, divide by 8, and round up to a whole number. The 3 is slices per person. The 8 is slices in a large pizza.

For 20 guests: 20 × 3 = 60 slices. 60 ÷ 8 = 7.5. Order 8 pizzas.

Quick table

When the rule gives the wrong answer

• Your pizzas are not 14-inch larges. The rule assumes 8 slices of a large. Eight slices of a 12-inch medium are a quarter less pizza, and eight slices of an 18-inch are two thirds more.
• Kids are coming. Children eat about 2 slices, not 3.
• There is other food. With wings, salad or cake, people eat about a quarter less pizza.
• The group is very hungry. Teenagers and sports teams average 4 slices.
• The crust is thin or deep. Thin crust is less filling, deep dish more.

The pizza calculator handles all five. It works from the actual area of the pizza you are ordering, not a slice count.

Where the 3 and the 8 come from

Three slices of a large pizza is about 58 square inches, a full meal for most adults. Eight is simply how most US pizzerias cut a 14-inch pie. If your shop cuts a large into 10 or 12, the slices are smaller and people eat more of them, but the number of pizzas you need stays the same.