Pizza Calculator
Tell us how many adults and kids are coming and the pizza size, and we will work out how many pizzas to order using the standard slice-per-guest rule.
Pizzas to order
2
- Total guests
- 6
- Slices needed
- 16
- Slices per pizza
- 10
- Slices ordered
- 20
- Slices left over
- 4
- Pizza per guest (sq in)
- 51.31
Slices per guest comes from the Pizza Today party-planning guide: 3 per adult and 2 per child for an average appetite, with light/hearty shifting by one slice. Slices per pizza follows standard pizzeria convention — 10″=6, 12″=8, 14″=10, 16″=12 — published by the major chains. Pizzas to order = ceil(total slices ÷ slices per pizza), so you never under-order. The square-inch line uses πr² as a sanity check on actual food volume per guest.
How to use this calculator
Enter the number of adults and kids (under 12), pick an appetite band — light (kids menu, lots of sides), average (the typical party), or hearty (teens, big eaters) — and choose the pizza size you plan to order. The headline number is how many whole pizzas to order; the breakdown shows total slices needed, slices left over and how much pizza each guest gets in square inches.
How the calculation works
The rule comes from Pizza Today magazine and the major US pizza chains: plan for 3 slices per adult and 2 slices per child of an average appetite, shifting one slice each way for light or hearty crowds. Slices per pizza is the standard pizzeria convention published by Domino's, Pizza Hut and Papa John's — 10″ small = 6 slices, 12″ medium = 8, 14″ large = 10, 16″ extra-large = 12. Total slices needed = adults × slices-per-adult + kids × slices-per-kid. Pizzas to order = ⌈total slices ÷ slices per pizza⌉, rounded up because you cannot buy a fractional pizza. The "pizza per guest in square inches" figure uses πr² as a sanity check on actual food volume per head.
Worked example
4 adults, 2 kids, average appetite, 14″ large pizzas. Slices needed = 3 × 4 + 2 × 2 = 12 + 4 = 16. A 14″ large is cut into 10 slices, so pizzas to order = ⌈16 ÷ 10⌉ = 2. That gives 20 slices ordered with 4 left over — about right for a small post-party snack. Pizza per guest = (π × 7² × 2) ÷ 6 ≈ 51 square inches, which is a generous helping. For comparison, two 12″ mediums would give only 16 slices (exactly enough, no leftovers) but only ≈ 38 sq in per guest, so most caterers prefer the larger size for the same headcount.
Frequently asked questions
How many pizzas do I need for 10 adults?
10 adults of an average appetite need 30 slices (3 each). For 14″ large pizzas (10 slices each) that is 3 pizzas exactly. For 12″ mediums (8 slices) you would round up to 4 pizzas and have 2 slices left over. For a hearty crowd (teenagers, athletes, late-night) plan for 4 slices per adult — that takes you to 40 slices, which is 4 large or 5 medium pizzas.
How many slices are in each pizza size?
Round pizzas follow the standard pizzeria slice count: 10″ personal/small = 6 slices, 12″ medium = 8 slices, 14″ large = 10 slices, 16″ extra-large = 12 slices. These are the cut patterns Domino's, Pizza Hut and Papa John's use, and they are what this calculator assumes. Some local pizzerias cut a large into 8 slices instead of 10 — if so the slices are bigger but the total pizza area is the same, so the headline pizza count stays the same.
Why is the leftover slices figure useful?
It tells you whether you are right on the edge of needing another pizza or comfortably over-catered. A result of "0 slices left over" means everyone gets exactly the average portion and no one can come back for seconds — risky if even one guest is unexpectedly hungry. Most party planners aim for 2–5 leftover slices on a 4-pizza order so you have a buffer without throwing food away. If your leftover count is double-digit you can usually drop a size.
What about adults who are dieting or kids who are picky?
Pick the "light" appetite — that drops the rule to 2 slices per adult and 1 per child, which is closer to a mixed buffet where pizza is one of several options. For a mixed crowd of dieters and big eaters, use "average" and just accept the leftovers — pizza reheats well and most parties under-order rather than over-order. If half the party is teenagers or athletes, go to "hearty" (4 adult, 3 kid).
Should I order a few different sizes or all the same?
For up to about 20 guests, all the same size (large) is simpler and most cost-effective per square inch. Above 20, mixing in one or two mediums lets you offer more topping variety without ordering a fourth or fifth large pizza. If a few guests have dietary needs (gluten-free, vegan, dairy-free) it is worth ordering a small dedicated pizza for them rather than trying to share — most chains charge a premium for GF crust but the per-slice cost is similar to a regular small.
Does this work for thin-crust vs deep-dish?
Yes — the slice counts are the same regardless of crust style, and slice count is what guests notice, not square inches. Deep-dish slices are physically heavier so guests will eat fewer; for a deep-dish or Chicago-style order, drop one slice off each appetite band (light becomes 1/0, average 2/1, hearty 3/2). The 14″ size is also less common in deep-dish — most deep-dish menus jump from 12″ to 16″.