Circumference of a circle, step by step
The circumference is the perimeter of a circle, and the whole difficulty is noticing which measurement you were handed.
The question
cm
Circumference: circle marked 4 cm
- The 4 cm marked here goes right ACROSS the circle — it is the diameter, the whole way across, which is exactly what a circumference needs.
- Circumference is π × the whole way across — that is the diameter, 4.
- Then multiply by π: 4 × 3.14 = 12.56 cm. Slightly more than three times across — which is what π has always been.
How it works.
- 01
The 4 cm marked here goes right ACROSS the circle — it is the diameter, the whole way across, which is exactly what a circumference needs.
- 02
Circumference is π × the whole way across — that is the diameter, 4.
- 03
Then multiply by π: 4 × 3.14 = 12.56 cm. Slightly more than three times across — which is what π has always been.