How to use it
- Choose what you know: radius, diameter, circumference or area.
- Enter the value in any unit; results use the same unit (squared for areas).
- For a rectangle, enter width and height.
Frequently asked questions
What is the formula for the area of a circle?
Area = π × r², where r is the radius. With the diameter: π × d² ÷ 4.
How do I get the diameter from the circumference?
Divide the circumference by π (about 3.14159). A 100 cm circumference means a diameter of 31.83 cm.
Which units does it use?
Whatever you type. If you enter centimeters, lengths are in cm and areas in cm².