Multiply the diameter by pi.
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The perimeter or circumference of a circle = diameter times pi
Its perimeter is half of its circumference plus its diameter
First you have to measure the diameter of the circle. The diameter is pi (pi is approximately 3.1415) times the diameter is the perimeter. Half the diameter is the radius and the area of a circle is pi times the radius squared. So for example, let us say that you have a circle with a diameter of 3 inches. The perimeter is then about 9.42 inches, and the area is about 7.07 square inches.
Let r be the radius of the circle. Then the perimeter of the half circle is pi*r + 2r. That is half of the circumference plus the diameter.
the perimeter is 3 times as long as the diameter Example: if my diameter is 7 inches long my perimeter is 3 times as much so it is 21 inches long