How this calculator works
Pizza is planned in slices per person, then rounded up to whole pizzas. Appetite changes the figure a lot: two and a half slices suits a mixed crowd with sides, while four and a half suits a crowd where pizza is the only food. The slices per pizza depends on how the shop cuts it, and a 16 inch pizza cut into 8 slices is twice the slice of a 10 inch cut into 8. The calorie estimate uses the slice count, the crust and topping type and the pizza size, scaling the energy of a slice by the square of the diameter from a 14 inch reference. The cost is the number of pizzas multiplied by the price. The plan rounds up, so there is usually a slice or two spare.
Formula
slices wanted = people x slices per person, where the appetite figures are 2.5, 3.5 and 4.5. pizzas = slices wanted / slices per pizza, rounded up. total slices = pizzas x slices per pizza. kcal per slice = crust kcal x topping factor x (pizza diameter / 35.6 cm)^2. calories = total slices x kcal per slice. cost = pizzas x price per pizza.
Worked example
For 12 hungry people the wanted slices are 12 x 3.5 = 42. At 8 slices a pizza that is 42 / 8 = 5.25, rounded up to 6 pizzas. The total is 48 slices, or 4 slices per person. Classic pepperoni slices at 285 x 1.05 = 299 kcal each give 48 x 299 = 14,350 kcal, about 1196 kcal per person. At $20 a pizza the cost is 6 x 20 = $120.
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Frequently asked questions
How many slices should I plan per person?
Two to three slices for a crowd eating with sides and talking, three to four for a hungry group, and four or more if pizza is the only food. Children often eat two. Ordering one extra pizza is usually cheaper than a second delivery.
How many pizzas for 20 people?
At a hungry 3.5 slices each, 20 people want 70 slices, which is 9 pizzas at 8 slices each. At moderate 2.5 slices each it is 50 slices, so 7 pizzas. Choose the appetite honestly; running out is the one outcome no one forgives.
Does the pizza size change the calories per slice?
Yes. A slice cut from a 16 inch pizza is much larger than one from a 10 inch pizza even though both are one eighth. The calorie figures here are per slice of a typical large pizza and scale with the crust and topping, so smaller pizzas will be lower per slice.
What if some guests are vegetarian?
Order at least one veggie pizza and keep it separate, with its own server. A mixed order with a veggie pizza for a third of the party is usually enough; ask in advance so the vegetarian guests are not left with salad.