How to work out a circle’s measurements
- Choose what you know: radius, diameter, circumference or area.
- Enter the value in any unit.
- Read the radius, diameter, circumference and area, in that unit and that unit squared.
Quick reference
| Radius | Diameter | Circumference | Area |
|---|---|---|---|
| 1 | 2 | 6.2832 | 3.1416 |
| 5 | 10 | 31.416 | 78.540 |
| 10 | 20 | 62.832 | 314.16 |
Pizza sizes
Because area grows with the square of the radius, a 16-inch pizza (area 201 in²) has almost twice the pizza of a 12-inch one (113 in²), not a third more. Compare areas, not diameters, when you’re checking which deal is better.