The 3/8 rule for ordering pizza
Pizza math is simple once you know the rule caterers and pizzerias use: three slices per adult, eight slices per large pizza. Multiply your guest count by 3/8 (0.375) and round up. Ten adults need 3.75 pizzas, so order four. Twenty adults need 7.5, so order eight. It's that easy for a plain adult crowd.
Real parties aren't plain adult crowds, which is why the calculator above asks who's coming. Kids under 12 usually manage two slices. Teenagers and athletes eat four, sometimes more. And if you're serving wings, breadsticks or salad alongside, most people drop a slice. A Super Bowl spread with dips, wings and pizza usually needs only one or two slices per person.
Pizza sizes and slice counts
Not all "slices" are equal. A 12-inch medium cut into eight slices gives you small slices; a 16-inch extra large cut into eight gives you enormous ones. The calculator handles this by converting everything to large-pizza slice equivalents based on area: a 14-inch large is the baseline (8 slices), a 12-inch medium is about three-quarters of that (6 large-slice equivalents), a 16–18-inch extra large is about 1.3× (10), and a 10-inch personal pizza is about half (4). Ordering extra larges is almost always the cheapest per slice.
Quick chart: how many large pizzas?
| Adults | Pizza only | With sides | Hungry crowd |
| 5 | 2 | 2 | 3 |
| 10 | 4 | 3 | 5 |
| 15 | 6 | 4 | 8 |
| 20 | 8 | 5 | 10 |
| 25 | 10 | 7 | 13 |
| 30 | 12 | 8 | 15 |
| 40 | 15 | 10 | 20 |
| 50 | 19 | 13 | 25 |
| 75 | 29 | 19 | 38 |
| 100 | 38 | 25 | 50 |
How to split the toppings
For a mixed crowd, a reliable split is 40% cheese, 30% pepperoni, 30% everything else (one veggie, one meat-lovers or specialty). Cheese and pepperoni get eaten first at almost every party. If kids are a big share of the headcount, push cheese to half. Always ask about allergies and have at least one option without pork.
What to serve with pizza
Wings are the classic partner: figure 5–6 wings per person alongside pizza, or use the wings calculator. A big green salad at one cup per person makes the meal feel complete and costs almost nothing. For drinks, plan two per person for the first hour and one per hour after; the drink calculator turns that into cans, bottles and ice.
Ordering tips
- Order 30–45 minutes before you want to eat; large orders can take longer, so call ahead for 10+ pizzas.
- Ask for pizzas to be cut into party-cut squares for kids' parties — it stretches each pie further and reduces waste.
- Keep a couple of pizzas boxed and closed until the first round is gone; open boxes go cold and get picked over.
- Leftover pizza should be refrigerated within two hours.
Frequently asked questions
How many pizzas for 20 people?
About 8 large pizzas with nothing else served, or 5 if there are wings and sides. Add two if it's a teenage crowd.
How many slices per person?
3 for adults, 2 for kids under 12, 4 for teens and athletes. Subtract one per person when you serve other food.
How many pizzas for 50 people?
About 19 large. With sides, 13–14.
How many pizzas for 30 kids?
About 8 large at two slices each, or 6 if you're also serving cake and snacks.
Is it cheaper to order large or extra large?
Almost always extra large. A 16-inch pizza has about 30% more pizza than a 14-inch for a much smaller price difference.
How many people does one large pizza feed?
Two to three adults, or four kids.