A calculator built around the number π (pi) — calculate a circle's area and circumference from its radius or diameter.
How to use this calculator
- Choose whether you're entering the radius or the diameter.
- Fill in the value.
- See the area and circumference calculated automatically using π.
Examples
r = 5 → Area = 78.54r = 5 → Circumference = 31.42
Frequently asked questions
Which value of π is used?
The calculator uses a precise value of π (JavaScript's built-in Math.PI) for accurate results.