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The 3/8 rule
The industry shorthand: 3 slices per adult, 8 slices per large — hence "3/8". Kids average 2 slices. This calculator applies those, adjusts for hunger, and always rounds up, because the failure modes aren't symmetric: leftover pizza is breakfast, missing pizza is a mutiny. The full guide has ready tables for 10–100 people and the mixed-topping strategy.
How many pizzas for 20 people?
20 adults × 3 slices = 60 slices ÷ 8 = 7.5 → order 8 large pizzas. If 5 of the 20 are kids: (15×3 + 5×2) = 55 slices → 7 larges.
What topping split should I order?
For a mixed crowd: 40% one-meat classics (pepperoni), 30% cheese/margherita, 20% veggie, 10% adventurous. Cheese is the universal fallback — never skip it.
Medium vs large — which is better value?
Almost always large: pizza area grows with the square of the diameter, so a 14-inch large has ~36% more pizza than a 12-inch medium but rarely costs 36% more.