What this calculator does
Pizza is sold by diameter and eaten by area, and the two do not move together. Area grows with the square of the diameter, so an 18 inch pizza is not twice a 9 inch one, it is four times. That gap between how a pizza is priced and how much of it there actually is, is where the value sits.
The practical consequence is that the largest size is almost always the best rate, and that two small pizzas are usually worse value than one large despite looking like more. This calculator works in area per dollar, which is the comparison that actually answers the question.
The formula
The area of each pizza is π times the square of half its diameter. Dividing that area by the price gives square inches per dollar, and the higher figure is the better value. The comparison of two of the first pizza against one of the second is included because it is the case people most often get wrong by eye.
| Term | Meaning |
|---|---|
| Area per dollar | Square inches of pizza for each dollar spent, the measure that makes different sizes comparable. |
| Diameter | The width across the pizza, which is how sizes are advertised even though area is what you eat. |
| Square relationship | Area grows with the square of the diameter, so a 50% larger diameter gives 125% more pizza. |
The inputs explained
| Field | What to enter |
|---|---|
| Pizza A: diameter (in) | The diameter of the first pizza, in inches. |
| Pizza A: price ($) | The price of the first pizza. |
| Pizza B: diameter (in) | The diameter of the second pizza, in inches. |
| Pizza B: price ($) | The price of the second pizza. |
When to use it
Choosing a size from a menu
Menu prices rise more slowly than area does, which is why the large is usually the better rate. Running the two sizes through settles it, and occasionally overturns the assumption when a small is on offer.
Deciding between two smalls and one large
Two 9 inch pizzas sound like more than one 13 inch, and they are not by much. The comparison line handles this case directly rather than leaving it to intuition, which is reliably wrong here.
Comparing any round item sold by diameter
Cakes, tortillas, pans and round tabletops all price by diameter and deliver area. The same calculation applies unchanged to any of them.
Worked examples
Every figure in the tables below is produced by this page’s own calculator at build time, so the numbers and the tool always agree. Select any row to load that scenario.
How much bigger is each pizza size, really?
A 9 inch pizza at $14 held fixed, compared against a $22 pizza at a range of diameters.
| Diameter of pizza B | Better value | B: area per dollar | B is bigger by |
|---|---|---|---|
| 9 in | Pizza A | 2.89 in² per $ | 0.000% |
| 11 in | Pizza A | 4.32 in² per $ | 49.4% |
| 13 in | Pizza B | 6.03 in² per $ | 108.6% |
| 15 in | Pizza B | 8.03 in² per $ | 177.8% |
| 18 in | Pizza B | 11.57 in² per $ | 300.0% |
Questions
Is a large pizza better value than two smalls?
Usually, and by more than it looks. Two 9 inch pizzas give 127.2 square inches, while a single 13 inch gives 132.7, so the one large pizza is already more food, and in the example above it costs $22 against $28. The larger the gap in diameter, the more decisively this holds.
Why does a small increase in diameter make such a difference?
Because area depends on the square of the diameter. Going from 9 to 13 inches is a 44% increase in width but a 109% increase in area. The number on the menu grows linearly while the pizza grows quadratically.
Does crust thickness affect the comparison?
It does, and this calculation ignores it. A thick base has more food per square inch than a thin one, and a wide crust edge means some of that area is not topped. For comparing the same style at different sizes it makes little difference; across quite different styles it is worth keeping in mind.
Does this work for square or rectangular pizzas?
Not directly, since the formula assumes a circle. For a rectangular one, multiply the two side lengths for the area and divide by the price yourself. The principle is identical, only the area formula changes.
For comparing packaged goods by weight or volume instead of area, see the unit price comparison calculator. For the price of something per kilogram, see the price per weight calculator.