To find the circumference of a circle, you can use one of two main formulas depending on whether you know the radius or the diameter of the circle:
- If you know the radius rrr:
Circumference=2πr\text{Circumference}=2\pi rCircumference=2πr
- If you know the diameter ddd:
Circumference=πd\text{Circumference}=\pi dCircumference=πd
Here, π\pi π (pi) is a mathematical constant approximately equal to 3.14159 (often approximated as 3.14 or 227\frac{22}{7}722).
Steps to calculate the circumference:
-
Find the radius or diameter of the circle.
The diameter is twice the radius: d=2rd=2rd=2r. -
Apply the appropriate formula:
- Multiply the radius by 2 and then by π\pi π, or
- Multiply the diameter directly by π\pi π.
-
Calculate the result.
For example, if the radius is 14 cm:
C=2×π×14=87.9646 cm (approximately)C=2\times \pi \times 14=87.9646\text{ cm (approximately)}C=2×π×14=87.9646 cm (approximately)
Alternatively, if the diameter is 28 cm:
C=π×28=87.9646 cm (approximately)C=\pi \times 28=87.9646\text{ cm (approximately)}C=π×28=87.9646 cm (approximately)
You can also measure the circumference physically by wrapping a string around the circle and then measuring the string length.
Summary:
Known Value| Formula for Circumference
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Radius rrr| C=2πrC=2\pi rC=2πr
Diameter ddd| C=πdC=\pi dC=πd
Use π≈3.14\pi \approx 3.14π≈3.14 for an estimation if a calculator is not available
