Circumference Calculator

Circumference of a circle

The circumference of a circle is the distance around its outer edge — basically the "perimeter" of the circle.

Formula

C = 2πr

(or equivalently C = πd)

Where:

• C = circumference
• r = radius (distance from center to any point on the edge)
• d = diameter (distance across the circle through the center = 2r)
• π (pi) ≈ 3.14159 (use 3.14 for quick calculations, or 22/7 for simple fractions)

Key relationships:

• Diameter is always twice the radius: d = 2r
• Radius is half the diameter: r = d/2
• The formula using the diameter is handy when the diameter is given directly.

Units are linear (e.g., cm, m, inches) — same as the radius or diameter.

Circumference of a circle calculations

Example 1 – Basic (using radius)
Radius = 7 cm
C = 2 × π × 7
C = 14π
C ≈ 14 × 3.14159
C ≈ 43.98 cm

Example 2 – Using diameter (quick method)
Diameter = 10 inches
C = π × d
C = π × 10
C ≈ 3.14159 × 10
C ≈ 31.42 inches