The diameter can be found by the formula: D = 2R, where the diameter is twice the radius of the circle.

The radius is the distance from the center to any point on the circle. Denoted by R.

If you know the radius of the circle, for example, it is equal to 8 cm, then D = 2 * 8 = 16 cm.
The second formula that you can find the diameter of a circle is: D = circumference divided by PI.

The number PI is used in mathematics to denote a particular irrational number, and is approximately 3,14.

If you know the circumference, for example, 18 cm, so D = 18 : 3,14 = 5,73 cm
So, very easy to find diameter of a circle.