Calculate Circle Properties Instantly
Find radius, diameter, circumference, and area from any one known value. Step-by-step solutions with formulas and visual diagram.
How It Works
C = 2πr, A = πr²All circle properties derive from the radius. Diameter = 2r. Circumference = 2πr. Area = πr². If you know any one property, you can calculate all others by first finding the radius.
Quick Tips
From Diameter
Radius = Diameter / 2. Then use standard formulas.
From Circumference
Radius = C / (2π). Then calculate area and diameter.
From Area
Radius = √(A / π). Then calculate circumference and diameter.
π ≈ 3.14159
For quick estimates: π ≈ 22/7 ≈ 3.14. Use the button for exact values.
Step-by-Step Instructions
- 1Select which value you know (radius, diameter, circumference, or area).
- 2Enter the known value.
- 3Click Calculate to see all circle properties.
Frequently Asked Questions
How do I find the area of a circle from the diameter?▼
First find the radius: r = diameter / 2. Then area = πr². For diameter 10: r = 5, area = π × 25 ≈ 78.54.
What is the relationship between circumference and diameter?▼
Circumference = π × diameter. This is the definition of π — the ratio of circumference to diameter is always π ≈ 3.14159 for any circle.
How do I find radius from area?▼
Radius = √(Area / π). For example, if area = 78.54, then r = √(78.54/3.14159) = √25 = 5.