[header] How to calculate the diameter of a circle [title] If you know the radius of the circle, double it to get the diameter. [step] The radius is the distance from the center of the circle to its edge. For example, if the radius of the circle is 4 cm, then the diameter of the circle is 4 cm x 2, or 8 cm. 
[title] If you know the circumference of the circle, divide it by π to get the diameter. [step] Π is equal to approximately 3.14 but you should use your calculator to get the most accurate results.