Circle Calculator
Area, circumference and diameter of a circle from its radius.
Area
78.5398
- Diameter10.0000
- Circumference31.4159
- Area78.5398
Inputs used
- Radius5
About this calculator
Everything about a circle follows from its radius: the diameter is twice the radius, the circumference is 2πr, and the area is πr². A circle with radius 5 has a diameter of 10, a circumference of about 31.42 and an area of about 78.54.
If you know the diameter instead, halve it for the radius. If you know the circumference, divide by 2π; if you know the area, the radius is √(area ÷ π).
A useful intuition: doubling the radius doubles the circumference but quadruples the area — which is why a 12-inch pizza is more than twice the pizza of an 8-inch one.
Results are informational only — not financial, medical or legal advice.