Circumference from the diameter
The question
cm
Circumference: circle marked 9 cm
How it works.
- 01
The 9 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, 9.
- 03
Then multiply by π: 9 × 3.14 = 28.26 cm. A little over three times across, as π says.