Pizza size calculator
Compare pizza diameters by real area.
Tools
Quick Calculators
Everyday calculators for questions that look simple but need the right formula: pizza size by area, age in days, coffee ratios, date differences. Instant results, no signup.
Last updated: May 2026
Tools in this section
Coffee ratio calculator
Scale a brew recipe without thinking.
Age calculator
Fast years-and-days age check.
Date difference
Count days between two dates.
Volume & liquid hub
Useful crossover section for kitchen-style conversions.
Each of these calculations looks straightforward but involves a formula most people do not carry in their head. A 14-inch pizza has 36 percent more area than a 12-inch, not 17 percent as the diameter alone suggests, because area grows with the square of the radius. A coffee recipe at 1:16 means 25 g of coffee per 400 ml of water, which is easy to get wrong when scaling. These tools solve the arithmetic precisely so you only have to enter the numbers.
How the maths works
Each calculator on this page solves a specific formula that is useful but not worth memorising. The table below shows what each one calculates and the core formula behind it.
| Calculator | What it solves | Core formula |
|---|---|---|
| Pizza size | Real area of a circular pizza | Area = pi x (diameter / 2) squared |
| Coffee ratio | Coffee dose for a brew volume | Grams of coffee = ml of water / ratio |
| Age in days | Exact age including leap years | Calendar days from birth date to today |
| Date difference | Days between any two dates | Calendar days between the two dates |
Pizza area is the clearest example of why these calculators are worth having. A 14-inch pizza has about 154 square inches of surface; a 12-inch has 113. The 14-inch is 36 percent more pizza, not 17 percent more as the diameter alone suggests. Area grows with the square of the diameter, so small size differences matter more than they look.
Getting more from each calculator
The pizza area result is the sharpest illustration of how intuition fails with circular things. Most people guess that a pizza 20 percent larger in diameter is about 20 percent more pizza. It is actually 44 percent more, because area scales with the square of the radius. A 16-inch pizza has 201 square inches; a 12-inch has 113. When a restaurant offers a deal on two medium pizzas versus one large, the area comparison is the only honest way to check if it is worth it.
Coffee brew ratios are counterintuitive in a different way. The ratio is grams of coffee per grams of water, not per cup volume. Recipes that say "2 tablespoons per 6 ounces" bake in assumptions about grind size and roast level that rarely match what you have at home. Working from a gram-based ratio (1:15 for strong, 1:17 for light) scales cleanly to any brew volume without guessing.
Date arithmetic matters most when you are working to a deadline or contract term. The difference between "30 calendar days" and "30 working days" can be a week or more. The date difference calculator returns raw calendar days; if you need working days, subtract weekends and public holidays from the result. For the age calculator, the leap-year handling is exact: it counts actual days elapsed, not years times 365, so the result is precise regardless of how many 29 Februaries fall in the period.
Frequently Asked Questions
Is one large pizza better value than two smaller ones?
Usually yes, because area grows with the square of the diameter. One 16-inch pizza is about 201 square inches, while two 11-inch pizzas total only about 190. The pizza size calculator compares any two sizes by real area.
What is a good coffee-to-water ratio?
A common starting point is 1 to 16, roughly 60 grams of coffee per litre of water. Use 1 to 15 for a stronger cup or 1 to 17 for a lighter one. The coffee ratio calculator scales it to your number of cups.
Does the age calculator handle leap years?
Yes. It counts the actual calendar days between the birth date and today, so leap days are included automatically and the result stays exact.
What can I use the date difference calculator for?
Counting the days to a deadline or holiday, working out how long a project ran, or how many days old something is. It returns the exact number of days between any two dates.
Do these calculators store any data?
No. They all run locally in your browser with no signup and nothing saved or sent, so you can use them freely and close the tab when you are done.
How does the pizza size calculator work?
It calculates real area using pi x radius squared, where the radius is half the diameter. A 14-inch pizza has an area of about 154 square inches; a 12-inch has 113. The gap is larger than the diameter difference suggests because area grows with the square of the size.
How do I scale a coffee recipe for more cups?
Multiply the total water volume by the inverse of your ratio. At 1:16, every 400 ml of water needs 25 g of coffee (400 / 16). The coffee ratio calculator scales any starting recipe to any number of servings instantly.
Why is calculating age in days useful?
Age in days is handy for comparing durations precisely, settling bets about who is older, or working out a deadline from a start date. The calculator accounts for leap years automatically, so the count is exact over any date range.