Circle measurements explained
Every measurement of a circle flows from its radius. The diameter is twice the radius, the circumference (the distance around) is 2πr, and the area (the space inside) is πr². Because they're all linked, knowing any one lets you work out the others — which is exactly what this calculator does, whichever value you start with.
Frequently asked questions
What is the area of a circle?
π multiplied by the radius squared (πr²). For a radius of 7, the area is about 153.94 square units.
What's the difference between circumference and diameter?
The diameter is the straight distance across the circle through its centre; the circumference is the distance all the way around the edge. Circumference is π times the diameter.
How do I find the radius from the area?
Divide the area by π, then take the square root. This tool does it for you — just pick "Area" as what you know.