Calculate the circumference (C) using the radius (R) of the circle. Use the formula: C = 2 x pi x R. Multiply the radius of the circle by twice the magnitude of the constant, pi. The radius is the length of any straight line measured from the center of the circle to the edge of the circle. Pi can be approximated to 3.14. For example, a circle with a radius of 10 cm has a circumference of C = 62.8 cm = 2 x 3.14 x 10 = 2 x pi x R.
Calculate the circumference (C) using the diameter (D) of the circle. Use the formula C = PI x D. Multiply the diameter of the circle by the constant, pi. (The diameter is the straight line measured through the center of the circle and extending in both directions to the edge of the circle.) For example, a circle with a diameter of 20 cm has a circumference of C = 62.8 cm = 3.14 x 20 = pi x D.
Calculate the circumference (C) using the area (A) of the circle. Use the formula C = (4 x PI x A)^(1/2). Multiply the area of the circle by four times the value of the constant pi, then find the square root of this product. For example, a circle with an area of 314 cm^2 has a circumference of C = 62.8 cm = (3942.8)^(1/2) = (4 x 3.14 x 314)^(1/2) = (4 x pi x A)^(1/2).