How Many Pizzas for 20 People?

The short answer for 20 people

For 20 adults with average appetites, order 8 large pizzas. A 16 inch pizza cuts into 8 slices, 20 adults eat about 3 slices each, and 60 slices divided by 8 comes to 7.5 pies. You round up, because a half pizza does not exist and running out is worse than having four slices left over.

That number moves for three reasons: who is eating, what else is on the table, and how big the pies are. Swap half the adults for kids and the count drops to about 5. Add a salad, wings and a cake and it drops again. Order 12 inch pizzas instead of 16 inch and you need closer to 8 pies that feed fewer people each, which is the part most people get wrong.

The rest of this page walks through the arithmetic so you can adjust it for your own crowd. The calculator above does the same thing with your numbers, including a cost per person at the end.

Slices per person: adults, kids and appetite

Pizza math starts with a slice count, not a pie count. Most pizza shops cut a 14 or 16 inch pie into 8 slices, and a 12 inch pie into 8 smaller ones. Plan on the following, then adjust for your crowd.

Three slices is the number to plan around for a mixed adult group, and it is generous enough to cover the person who goes back for a fourth. A crowd that skews toward women in their thirties and forties often eats closer to 2.5, and a crew of college athletes can clear 5 each without slowing down.

Children are the biggest source of over ordering. A six year old eats one slice and half of another, so a party with 10 kids and 10 adults needs the food of 15 adults, not 20. Teenagers are the exception in the other direction. Treat anyone over 13 as a hearty adult and your estimate stops being short.

Why a 16 inch pizza is not a third bigger than a 12 inch

Diameter grows in a straight line. Area grows with the square of the diameter, because a pizza is a circle and the area is 3.14 times the radius squared. That single fact explains most bad pizza orders.

A 16 inch pizza is 33% wider than a 12 inch, but it holds 78% more pizza. Two 12 inch pies give you 226 square inches. One 16 inch gives 201. So two 12s beat one 16 by a small margin, while three 12s lose badly to two 16s, which is 339 against 402 square inches.

Price usually tracks the area, not the diameter, which is why the 16 inch is almost always the better deal per square inch. Check it once at your local shop: divide the price by the area. A 16 inch at $18 is 9 cents per square inch, and a 12 inch at $13 is 11.5 cents. The bigger pie wins even though the sticker shocks people.

Slice count is the catch. If a shop cuts a 16 inch into 8 slices, each slice is 25 square inches, which is a big slice. Guests take fewer slices of a big pie, so the slice based estimate above already accounts for it. Do not double count by assuming 8 slices of a 16 inch equals 8 slices of a 12 inch.

A worked example: 12 adults and 8 kids with a side

Twelve adults, eight kids, one side dish, 14 inch pizzas at $16 each.

• Adult slices: 12 x 3 = 36
• Kid slices: 8 x 1.5 = 12
• Total before sides: 48 slices
• One side dish trims appetite by 20%: 48 x 0.8 = 38.4 slices
• 14 inch pizzas cut into 8: 38.4 divided by 8 = 4.8, so 5 pizzas
• Pizza on hand: 5 x 8 = 40 slices, about 1.6 slices spare
• Area on the table: 5 x 154 = 770 square inches, or 38.5 per person
• Cost: 5 x $16 = $80, or $4 per person

The same party without the side dish needs 48 slices, which is exactly 6 pizzas. That is a $16 difference from one bowl of salad, and it is why the side question belongs in the calculator rather than in your head at the counter.

Order the same 48 slices as 16 inch pies and you get 6 pizzas at 8 slices each, but 1,206 square inches instead of 924. Same slice count, 30% more food. The 16 inch is the safer choice for a hungry crowd, and the 14 inch is the better choice when you want the slices to look generous without overbuying.

Sides, apps and cake change the count

Pizza is rarely the only food at a party for 20. Every additional dish takes pressure off the pies, and the effect is larger than most hosts expect.

• One side dish such as a salad, garlic knots or wings: cut the pizza estimate by 20%.
• Two or more sides plus dessert: cut it by 35%.
• A full meal before the pizza, such as a cookout: cut it by half and treat pizza as a late snack.
• Cake or ice cream afterward: another 5% to 10% off, mostly because people stop at two slices to save room.

Wings are the side that fools people. A dozen wings is roughly the food value of a slice and a half per person for a group of four, so two dozen wings for 20 people barely registers. A tray of lasagna or a pot of chili does register, and it can cut the pizza order in half.

Alcohol works the other way. A crowd drinking beer eats more pizza than the same crowd drinking water, partly because the evening runs longer and partly because salty food goes with beer. If the party is a game night with drinks, add 10% to the slice count rather than subtracting for sides.

Order fewer kinds and more pies

Variety is where orders get expensive and slow. Six different pizzas means six partial pies, and a partial pie of an unpopular topping is the one that gets thrown out.

Three varieties covers almost any crowd: a cheese or pepperoni for the cautious eaters, a vegetable for the adults, and one meat heavy option. Order them in the ratio 2 to 1 to 1 for a group of 20. If you know the crowd, four varieties is the ceiling, and only if each one has at least five people who will eat it.

Half and half is the better tool for a divided crowd. Most shops will make a pie with one topping on each half for the same price, which turns one pizza into two options without adding a partial pie. Ask for it when you order rather than at pickup, because the till has to be set up for it.

Specialty pies also cost more per square inch and slow the kitchen down. A plain cheese pizza takes less time to make than a five topping one, and a large order of simple pies arrives hotter. If the party has a start time, simple pies are the practical choice.

Leftovers, timing and delivery

Order for the crowd plus a small buffer, not for the crowd plus a large one. A 10% buffer is four extra slices on a 40 slice order, which covers the guest who arrives hungry without leaving you with two whole pies.

Pizza holds up better than most party food, which makes a small overbuy cheap insurance. Leftover slices keep 3 to 4 days in the refrigerator in a sealed container, and they reheat best in a skillet or an oven at 350 degrees F for 6 to 8 minutes. A microwave works but turns the crust rubbery. The USDA's food safety guidance on leftovers puts the refrigerator limit at 3 to 4 days for cooked food, and pizza is no exception.

Timing matters as much as quantity. Twenty pizzas worth of food does not fit in one oven, so delivery is the realistic option above 6 pies. Order 45 to 60 minutes before you want to eat on a weekend, and ask for a stagger: half the pies at the start time, half 20 minutes later. Cold pizza at 7pm and hot pizza at 7:40 beats 10 pies going cold on the counter at once.

Ask for the pies uncut if you plan to serve them on a buffet, then cut them into smaller squares. A 16 inch pie cut into 16 squares feeds a grazing crowd longer than 8 wedges, because people take two small pieces instead of one big one.

Cost per person and how to split it

Pizza is one of the few party foods where the cost per person is easy to predict. At $18 for a 16 inch pie, 8 pies feed 20 adults for $144, or $7.20 each. Add a salad and a two liter bottle of soda and you are near $8.50 per person.

Cost per person stays flat because the pizza count scales with the head count, with one exception: the last row rounds down from 15 pizzas exactly, so a group of 40 gets a small break. Larger groups also qualify for shop discounts, and a 10 pie order is worth asking about even when the menu does not mention one.

If you are splitting the bill, charge by the slice rather than by the pie. Twenty people and 64 slices is 3.2 slices per person, and a household of four that ate 12 slices owes for 12, not for a quarter of the total. The USDA's MyPlate guidance is a reasonable check on portions if you want a second opinion on how much food a crowd needs, though it measures in cups rather than slices.