How it is calculated
Area is πr², circumference is 2πr, and diameter is twice the radius. When the area is known, the radius is the square root of S/π.
S = πr²
Where the numbers come from
- What is known
- Value
Example
Radius 10. Area π × 10² ≈ 314,16. Circumference 2π × 10 ≈ 62,83.
Questions
Which value of π is used?
JavaScript’s built-in number, about 15 significant digits. That covers a school exercise. For a drawing, watch the rounding on the screen.
Can I enter the diameter instead of the radius?
Yes, switch “What is known”.
Which units of measure?
Any units, as long as they match. If the radius is in centimetres, the area is in square centimetres.