Mensuration · JSS 1
Circumference of a circle
Find the distance round a circle.
- C = 2πr = πd
What the letters mean
- r
- the radius
- d
- the diameter (2r)
- π
- pi ≈ 227 or 3.142
Worked example
Find the circumference of a circle of radius 7 cm (π = 227).
Step 1: Use 2πr
C = 2 × 227 × 7 = 44 cm
Final answer: 44 cm
See it
Play with this picture from the Perimeter of Plane Shapes lesson.
P = 2 × (5 + 3) = 16 cm
Walk round the edge: 16 one-centimetre steps. (Area would be 15 cm².) Drag the blue corner.
Length5 cm
Height3 cm