Circumference is calculated with C = π × d, where d is the diameter. For example, a circle with diameter 10 has circumference π × 10 ≈ 31.42.

Diameter is calculated with d = C ÷ π. For example, if circumference is 31.42, diameter is 31.42 ÷ π ≈ 10.

Radius is half the diameter: r = d ÷ 2. For example, if diameter is 10, radius is 5.

Radius is calculated with r = C ÷ (2 × π). For example, if circumference is 31.42, radius is 31.42 ÷ (2π) ≈ 5.