To find the circumference of a circle, you use one of these two formulas:
- C=π×dC=\pi \times dC=π×d, where ddd is the diameter of the circle.
- C=2×π×rC=2\times \pi \times rC=2×π×r, where rrr is the radius of the circle.
Here, π\pi π (pi) is a constant approximately equal to 3.14.
Steps to calculate circumference:
- If you know the radius, multiply it by 2 to get the diameter, or use the radius directly in the formula C=2πrC=2\pi rC=2πr.
- If you know the diameter, multiply it directly by π\pi π.
- Use π≈3.14\pi \approx 3.14π≈3.14 for an approximate value.
- The result will give you the length around the circle, called the circumference.
Example:
- For a circle with radius 9 cm:
C=2×π×9=18π≈56.52 cmC=2\times \pi \times 9=18\pi \approx 56.52\text{ cm}C=2×π×9=18π≈56.52 cm
- For a circle with diameter 12 feet:
C=π×12=12π≈37.68 feetC=\pi \times 12=12\pi \approx 37.68\text{ feet}C=π×12=12π≈37.68 feet
You can also measure the circumference physically by wrapping a string around the circle and measuring the string length
