Pizza Size Value Calculator

Pizza size chart: how many square inches in each size

A menu lists pizzas by diameter, but what you eat is the area, which is pi times the radius squared. The radius is half the diameter, so a 12 inch pizza is pi times 6 squared, or 113.1 square inches. Because the radius is squared, the food climbs much faster than the width: a 20 inch pizza is twice the diameter of a 10 inch but 4.00 times the pizza.

Is a 12 inch pizza the radius or the diameter?

It is the diameter, the full width across the middle. Every menu size works that way, so a 12 inch pizza is 12 inches from edge to edge and its radius is 6 inches. This matters because the area formula wants the radius, not the number printed on the menu, and halving it is the step people miss. A 12 inch pizza is pi times 6 squared, which is 113.1 square inches. Feed the 12 straight into the formula instead and you get 452.4 square inches, four times too much pizza.

Two more places the same slip shows up. Boxes are square and always a little wider than the pizza, so a 12 inch box does not hold 12 inches of food. And a deep pan or stuffed crust of the same stated size gives you less usable surface than a thin base, because more of that width goes into the rim. The tables here measure the flat circle only.

Pizza sizes in centimetres

Menus across Europe list the diameter in centimetres instead, and the two scales do not line up on round numbers. One inch is exactly 2.54 cm, so a 7 inch pizza is 17.78 cm and a 30 cm pizza is 11.8 inches rather than a clean 12. Read this table in either direction to place a metric size against the inch sizes you know.

How big is one slice?

Cutting a pizza into more pieces does not make more pizza, so a slice is just the area divided by the number of cuts. The useful consequence is that slice counts make sizes look comparable when they are not. A 16 inch cut into 8 gives 25.1 square inches a slice, while a 12 inch cut into the same 8 gives 14.1. Two slices of the small one are still less food than one and a half of the large.

Per-slice figures are the whole area shared equally, which is what a straight cut through the centre gives. Square-cut or party-cut pizzas break that up: the middle pieces are full squares and the edge pieces are small offcuts, so the average still holds but no single piece matches it.

Two smaller pizzas versus one larger one

Two boxes look like more food than one, and sometimes they are, but the answer flips depending on the exact pair. Two 12 inch pizzas beat a single 16 inch by area, yet the same two lose to one 18 inch. These rows compare total area only, so they answer which option is more pizza. Which one is better value also depends on price, and that is what the calculator above settles.

Is the upsize worth it? The break-even price for each step

Going up a size is worth it whenever the extra pizza outruns the extra cost. Since the area ratio between two sizes is fixed, so is the price at which the two are exactly equal value. Going from 12 inch to 16 inch gives you 1.78 times the pizza, so the 16 inch is the better deal at any price under 1.78 times the 12 inch. The last column puts that in cash by assuming the smaller pizza costs £10.00. Swap in the prices on your own menu with the calculator above.

Every figure on this page is computed from the area formula rather than typed in, so the tables match the calculator exactly. They compare flat round pizzas and ignore crust thickness, toppings and how much of the edge you actually eat. For the geometry on its own see the circle calculator, and for the same price-per-unit test on anything else sold by size there is the unit price calculator.