How it works
- Diameter = 2 × radius.
- Circumference = 2 × π × radius (or π × diameter).
- Area = π × radius².
- Working backwards: radius = circumference ÷ 2π, or √(area ÷ π).
Frequently asked questions
What value of π is used?
Full precision (3.14159265…), not 3.14, so answers are accurate. Steps also show answers as multiples of π, such as 25π.
Why is the area unit squared?
Area measures a surface, so a radius in cm gives an area in cm².
Results are estimates for general information and are not financial, medical or professional advice.