How to use the circle calculator
Find area, circumference and diameter from the radius. Enter radius in the field above; the diameter, circumference, area are computed instantly and plotted on the chart so you can see how the answer changes.
Formula
Variables
- r — Radius
Worked example
With radius = 5, the calculator gives diameter ≈ 10; circumference ≈ 31.41593; area ≈ 78.53982.
Frequently asked questions
What is the formula for the circle calculation?
Diameter = 2 × r. Circumference = 2 × π × r. Area = π × r × r. Here r is radius.
What inputs do I need for the circle calculator?
You need radius. Each field is pre-filled with a typical example so you can see how the result responds as you edit the numbers.
How do I use this calculator?
Type values into the input fields. Results and the chart update instantly. Use Reset to restore the example values, Copy results to paste them elsewhere, or Share to copy a link that preserves your inputs.
Is the result exact?
Calculations use standard formulas and double-precision arithmetic, then display about seven significant figures. Real-world measurements carry uncertainty, so treat results as estimates unless your inputs are exact.