🧱 See It
Picture a bicycle wheel rolling one full turn. The distance it travels along the ground in that single rotation is exactly the distance around the outside edge of the wheel — that distance is called the circumference.
Every circle has two key measurements for its size: the diameter (a straight line across the circle, passing right through the center) and the radius (a straight line from the center out to the edge — exactly half the diameter).
✏️ Draw It
The radius (4 cm) is just the right half of the diameter line (8 cm) — diameter is always 2 × radius, no matter how big or small the circle is.
🔢 Write It
Circumference = 3.14 × diameter
(also written C = πd)
Circumference = 2 × 3.14 × radius
💡 Worked Examples
Example 1 — Circle with diameter: 10 cm
- Formula:
C = 3.14 × diameter - Plug in:
C = 3.14 × 10 - Multiply:
C = 31.4 - Answer:
C = 31.4 cm
Example 2 — Circle with radius: 7 cm
- Only the radius is given — find the diameter first:
diameter = 2 × 7 = 14 cm - Formula:
C = 3.14 × diameter - Plug in:
C = 3.14 × 14 - Multiply:
C = 43.96 - Answer:
C = 43.96 cm
🧠 Quick Reference
Quick reminder: diameter = 2 × radius