Divide the circumference by pi, approximately 3.14, to calculate the diameter of the circle. For example, if the circumference equals 56.52 inches, divide 56.52 by 3.14 to get a diameter of 18 inches.
Multiply the radius by 2 to find the diameter. For example, if you have a radius of 47 inches, multiply 47 by 2 to get a diameter of 94 inches.
Divide the radius by 0.5 to calculate the diameter. In this example, check your answer by dividing 47 by 0.5 to verify your answer of 94 inches.