Pizza Size Calculator

How pizza size really works

A pizza's area is π × r², where r is half the diameter. Because the radius is squared, area grows much faster than diameter: a 16-inch pizza is only 4 inches wider than a 12-inch one but has 78% more pizza (201.1 vs 113.1 square inches).

Pizza sizes and areas

Slice counts and servings vary by pizzeria and appetite; treat them as a starting point.

One large pizza or two mediums?

The single 18-inch pizza gives 12.5% more pizza for $4 less – about 26% cheaper per square inch. One 18-inch pizza equals 2.25 twelve-inch pizzas. Two mediums only win when you need two different toppings or the deal price is very low.

How to compare pizza prices

1. Work out the area of each pizza: π × (diameter ÷ 2)².
2. Multiply by the number of pizzas in each option.
3. Divide the total price by the total area.
4. The lowest price per square inch is the best value.

Don't forget the crust

If you mostly care about the topped part, subtract the crust. A 14-inch pizza with a 1-inch crust has a topped circle 12 inches across: 113.1 square inches out of 153.9 – about 73%. On small pizzas the crust is a bigger share, which makes large pizzas even better value for topping lovers.

How many pizzas do I need?

Multiply the number of people by slices per person, then divide by slices per pizza and round up. A common rule of thumb is 2–3 slices per adult and 1–2 per child, but sports teams and teenagers may eat more.

Example: 12 adults × 3 slices = 36 slices. With 8-slice pizzas you need 36 ÷ 8 = 4.5, so order 5 pizzas.

Rectangular and sheet pizzas

For rectangular pizzas multiply length by width. A 12 × 18-inch half-sheet is 216 square inches – a little less than one 18-inch round (254.5) and almost twice a 12-inch round.

Price per square inch at typical prices

In this example each step up in size lowers the price per square inch; the 16-inch pizza costs about 22% less per square inch than the 10-inch. Plug in your local menu prices to check.

Price per slice

Divide the price by the number of slices. An $18, 16-inch pizza cut into 8 slices is $2.25 a slice; each slice has about 25.1 square inches. A $9, 10-inch pizza in 6 slices is $1.50 a slice but each slice is only 13.1 square inches – so the bigger slice is better value even though it costs more.

Judging pizza deals

• 'Buy one, get one free' halves the price per square inch – compare it with the large-size price, not the menu price of one pizza.
• Combo deals with sides or drinks are only good value if you would have ordered those items anyway.
• Check whether a 'large' at one pizzeria is the same size as a 'large' elsewhere – it can range from 13 to 16 inches.
• Delivery fees and tips add to the real cost; include them when comparing options.

How much pizza for different events

These are rules of thumb – order one extra pizza if running out would be a problem, or one fewer if there is plenty of other food.

Neapolitan and metric sizes

Traditional Neapolitan pizzas are made no larger than about 35 cm across, and many pizzerias outside the US sell 30–33 cm pizzas. A 30 cm pizza has an area of about 707 cm², almost the same as a 12-inch pizza (729.7 cm²).

Pizza size equivalents

Ratios come straight from the square of the diameters: (16 ÷ 12)² = 1.78. Doubling the diameter always gives four times the pizza.

Square vs round pizza

A 12-inch square pizza has 144 square inches – 27% more than a 12-inch round (113.1). When a menu lists a square or Detroit-style pizza by side length, compare it by area, not by the number in its name.

Working out pizza area by hand

1. Halve the diameter to get the radius (a 12-inch pizza has a 6-inch radius).
2. Square the radius: 6 × 6 = 36.
3. Multiply by π (3.1416): 36 × 3.1416 = 113.1 square inches.