Circumference from the diameter, step by step
The circumference is pi times the diameter.
The question
cm
Circumference: circle marked 9 cm
- 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.
- Circumference is π × the whole way across — that is the diameter, 9.
- Then multiply by π: 9 × 3.14 = 28.26 cm. Slightly more than three times across — which is what π has always been.
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. Slightly more than three times across — which is what π has always been.