Pizza Size Calculator

About the Pizza Size Calculator

Pizza menus sell pizzas by their diameter — 10, 12, 14, 16 or 18 inches — and most people compare them as if a 16-inch pizza were just a little bigger than a 12-inch one. It is not. What you eat is the area of the pizza, and area grows with the square of the diameter. Four extra inches across turn out to mean three quarters more pizza. That makes the bigger sizes much better value than they look, and it means that "two mediums for the price of one large" deals are often not the bargain they seem.

This pizza size calculator compares any two offers. Enter the size, the price and the number of pizzas in each — a single large, two mediums, a family deal — in inches or centimetres. It shows the area of each offer, the price per square inch (or per 100 cm²), which one is the better deal and by how much, how much more pizza one offer has than the other, and what the second offer would have to cost to be equal value.

How to Use the Pizza Size Calculator

Choose whether the sizes are in inches or centimetres.

For offer A, enter the diameter of the pizza, the total price of the offer, and how many pizzas it includes.

Enter the same for offer B.

The result updates as you type, so you can try several menu options quickly.

How Pizza Value Is Worked Out

  area of one pizza   =  π × (diameter ÷ 2)²
  area of an offer    =  area of one pizza × number of pizzas
  price per sq in     =  price of the offer ÷ area of the offer
  saving              =  1 − cheaper price per area ÷ dearer price per area

Step-by-Step Example

A 12-inch pizza for 12.00 against a 16-inch pizza for 18.00.

  Area A:   π × 6²                     =  113 sq in
  Area B:   π × 8²                     =  201 sq in
  Value A:  12.00 ÷ 113.1              =  0.1061 per sq in
  Value B:  18.00 ÷ 201.1              =  0.0895 per sq in
  Saving:   1 − 0.0895 ÷ 0.1061        =  15.6% cheaper for the 16-inch

The 16-inch pizza has 1.78 times as much pizza. At the 12-inch price per square inch it would cost 21.33, so 18.00 is a good deal.

Two 12-inch pizzas for 20.00 against one 18-inch pizza for 20.00.

  Area A:   2 × π × 6²                 =  226 sq in
  Area B:   π × 9²                     =  254 sq in

For the same money, the single 18-inch pizza gives about 12.5% more to eat.

Pizza Areas at a Glance

In centimetres, a 25 cm pizza is about 491 cm², a 30 cm pizza 707 cm², a 35 cm pizza 962 cm² and a 40 cm pizza 1,257 cm².

Why Our Intuition Gets Pizza Wrong

People tend to judge size by width, which grows in a straight line, rather than by area, which grows much faster. Doubling the diameter of a pizza gives four times as much pizza, not twice as much. The effect is the same reason a 55-inch television looks so much larger than a 40-inch one. Pizza restaurants know this: the cost of dough, sauce and cheese rises with area, but the cost of making, boxing and delivering the pizza hardly changes with size, so larger pizzas are usually priced to give far more per pound or dollar.

The Crust Effect

A pizza's crust is a ring of roughly constant width around the edge. On a small pizza that ring is a large share of the whole; on a big one it is a much smaller share. A 10-inch pizza with a 1-inch crust has only 50 square inches of topped pizza out of 79, about 64 percent, while an 18-inch pizza with the same crust has 201 out of 254, about 79 percent. So if you care most about the toppings, the advantage of a large pizza is even greater than the area comparison shows.

Ordering for a Group

As a rough guide, most adults eat two to three slices of a 12 to 14-inch pizza, which is around 75 to 100 square inches each. A 16-inch pizza cut into eight slices feeds about three adults, and an 18-inch pizza about three to four. Children and lighter eaters need less; teenagers and hungry adults need more. When ordering several pizzas for a party, choose the largest size offered and vary the toppings across them, rather than ordering lots of small pizzas.

When Smaller Can Still Make Sense

Value per square inch is not everything. Smaller pizzas let everyone choose their own toppings, suit dietary needs such as gluten-free or vegan bases, and waste less if people will not finish a large one. Some deals also add sides or drinks that are worth something to you. The calculator shows the pure pizza value; the rest is up to your table.

Understanding Your Result

Better deal names the offer with the lower price per unit of area.

Pizza area gives the total area of each offer.

Price per area gives the price per square inch, or per 100 cm².

Saving shows how much cheaper, per unit of area, the better offer is.

How much more pizza compares the total amount in offer B with offer A.

Fair price for B shows what offer B would cost at offer A's value.

Worth knowing gives the classic two-mediums-or-one-large comparison.

When Should You Use This Calculator?

Choosing between sizes on a takeaway menu.

Checking a meal deal of several smaller pizzas.

Ordering for a party or office lunch.

Comparing restaurants with different size ranges.

Settling a debate about which pizza is really bigger.

Common Mistakes

Comparing pizzas by diameter instead of area.

Assuming two mediums beat one large.

Forgetting to enter the number of pizzas in a multi-pizza deal.

Mixing inches and centimetres between the two offers.

Ignoring the crust, which takes a bigger share of small pizzas.