Pizza Party Calculator
How many pizzas to order for your guests — sized by how much pizza they actually eat, not by a flat slice count.
What Domino's, Pizza Hut and Papa John's all call a large.
4
pizzas — large — 14", 8 slices each
Split the order across toppings. The shares are relative, so 2 / 2 / 1 and 40 / 40 / 20 mean the same thing.
Ordering pizza for a group is one calculation with one trap in it. The calculation is easy: decide how much each guest eats, add it up, divide by how much a pizza holds. The trap is that a slice is not a unit of anything — a slice of a 10-inch small is 13 square inches and a slice of an 18-inch party pizza is 21, so "three slices each" describes two very different meals depending on what you order.
This calculator settles that by working in area. Appetite is quoted in the unit everyone already thinks in — slices of a 14-inch large, cut into eight, which is about 19 square inches each — and then converted to the size you actually picked. A light eater is 2 of those, an average eater 3, a hearty eater 4, and a child counts as half an adult. Those are the conventional planning figures the whole category uses; they are a rule of thumb for ordering, not a measurement of anyone's appetite, so nudge the appetite setting if you know your crowd.
The pizza count is then rounded up to a whole pizza, because that is what you can buy, and the slices that rounding bought you are reported as leftovers rather than quietly absorbed. If you actively want leftovers, the leftovers setting adds to the demand before the rounding instead of after it.
What the sizes actually are. "Large" is a marketing word, not a measurement, but the big three happen to agree: a large is 14 inches at Domino's, Pizza Hut and Papa John's alike, cut into 8. That is why it is the size this calculator quotes appetite in. The one that breaks the pattern is Costco's food court pizza, which is 18 inches — 254 square inches against a large's 154, so one Costco pizza is about 1.65 large pizzas, and it is cut into 12 rather than 8.
| Pizza | Diameter | Slices | Area | Average adults it feeds |
|---|---|---|---|---|
| Small | 10″ | 6 | 79 in² | 1 |
| Medium | 12″ | 8 | 113 in² | 1 |
| Large — Domino's, Pizza Hut, Papa John's | 14″ | 8 | 154 in² | 2 |
| Extra large — Papa John's | 16″ | 10 | 201 in² | 3 |
| Costco food court | 18″ | 12 | 254 in² | 4 |
Worked examples (all on 14-inch larges cut into 8, unless said otherwise):
- 8 adults and 4 kids with average appetites eat 30 slices, so you order 4 pizzas — 32 slices, with 2 left over.
- The same 30 slices' worth of pizza on 10-inch smalls cut into 6 is 8 pizzas, not 5. The slices are two thirds the size, so you need 45 of them.
- 20 hearty adults with a 25% leftovers allowance need 100 slices — 13 pizzas, leaving 4 slices spare.
- 6 adults and 6 kids eating light is 3 pizzas, and 6 of those 24 slices go home with somebody.
- 20 average adults is 8 larges — or 5 Costco pizzas. Same amount of pizza, three fewer boxes.
The topping breakdown splits whole pizzas by largest remainder: every topping's exact share is rounded down first, then the pizzas that rounding left over go to the toppings with the biggest fractional parts. The rows therefore always add up to the order, so you never have to work out which line the missing pizza went to. When there are more toppings than pizzas, the calculator says which ones got nothing instead of hiding the shortfall.
How big is a Costco pizza?
Costco's food court pizza is 18 inches across and cut into 12 slices — 254 square inches of pizza, which is about 1.65 times a 14-inch large from Domino's, Pizza Hut or Papa John's. Because it is cut into 12 rather than 8, each slice is 21 square inches against a large's 19, so a Costco slice is a little bigger too. On this calculator's figures one whole pie feeds 4 adults with average appetites — 3 if they are hungry, 6 if they are eating light alongside other food, which is where the widely quoted "serves 5 to 6" lands.
How many Costco pizzas do I need for a party?
Pick "Party / Costco — 18\"" as the size and the calculator does it for you, but as a rule of thumb: one pizza per 4 average adults. 20 adults is 5 pizzas, 30 adults is 7. That is meaningfully fewer boxes than the same party on 14-inch larges, which would take 8 and 12 — an 18-inch pizza is 65% more pizza than a 14-inch one, not 29% more as the diameters suggest.
How many slices are in a large Domino's, Pizza Hut or Papa John's pizza?
All three cut a 14-inch large into 8 slices, which is why this calculator uses that as its reference size. Papa John's extra large is 16 inches cut into 10. Sizes below large vary more between chains than the large does, and any of them will cut a pizza differently if you ask — the slices-per-pizza field is editable for exactly that reason.
How many pizzas do I need for 20 people?
For 20 adults with average appetites, ordering 14-inch larges cut into 8 slices, you need 60 slices — 8 pizzas, which gives you 64 slices and 4 spare. Swap in kids for adults and it drops fast: 10 adults and 10 kids is 45 slices, or 6 pizzas. If you want leftovers to send home, add the 25% allowance and 20 adults becomes 10 pizzas.
How many slices are in a pizza?
It depends on the size and the shop, which is why this calculator lets you override it. The common cuts are 6 slices on a 10-inch small, 8 on a 12-inch medium, 8 on a 14-inch large, 10 on a 16-inch extra large and 12 on an 18-inch party pizza. Ask when you order if it matters — some places cut a large into 10, which makes each slice a fifth smaller than the calculator's default assumes.
Is one large pizza more than two smalls?
Usually, and by more than people expect, because area grows with the square of the diameter. One 18-inch pizza is 254 square inches against 226 for two 12-inch mediums, so the single 18-inch is the bigger order — and normally the cheaper one. But the rule is not universal: two 12-inch mediums beat one 16-inch extra large, which is 201 square inches. Compare the areas rather than the diameters.
How much pizza does a child eat?
This calculator counts a child as half an adult at the same appetite setting — 1.5 slices of a 14-inch large on the average setting, against 3 for an adult. That is a planning average across a wide age range, so a party of teenagers is better entered as adults, and a party of toddlers is better entered as kids on the light setting.
Should I order extra for leftovers?
The rounding up to whole pizzas already gives you a few spare slices most of the time — the default 8 adults and 4 kids comes out with 2. The leftovers setting is for when you actively want people to take pizza home, or when the party runs long enough for a second round. It adds to the demand before the rounding, so a 25% allowance is 25% more pizza rather than 25% more slices left in the boxes.
Can I share my order with the people I am ordering with?
Yes — the whole thing lives in the page URL, so the Copy link button gives you a link that reopens the calculator with your guest count, size, appetite and topping split already filled in. Nothing is sent to a server; the state travels in the part of the URL after the # that browsers never transmit.
Related Tools
Updated August 22, 2026