To find the perimeter of a circle, which is also called the circumference, you use one of these formulas depending on what measurement you have:

• If you know the radius rrr, the formula is:

Perimeter=2πr\text{Perimeter}=2\pi rPerimeter=2πr

• If you know the diameter ddd, the formula is:

Perimeter=πd\text{Perimeter}=\pi dPerimeter=πd

Here, π\pi π (pi) is a constant approximately equal to 3.14159.

Steps to calculate the perimeter:

1. Identify the radius or diameter of the circle.
2. Use the appropriate formula:
   • Use 2πr2\pi r2πr if you have the radius.
   • Use πd\pi dπd if you have the diameter.
3. Multiply to get the perimeter (circumference).

Example:

If the radius is 7 cm, the perimeter is:

2×3.14159×7≈43.98 cm2\times 3.14159\times 7\approx 43.98\text{ cm}2×3.14159×7≈43.98 cm

If the diameter is 10 meters, the perimeter is:

3.14159×10=31.42 meters3.14159\times 10=31.42\text{ meters}3.14159×10=31.42 meters

This perimeter represents the total distance around the circle