# The radius of the circle is 4 cm, which is equal to the diameter of this circle.

In order to find out what the diameter of a circle is, if you know its radius, you should remember the rule.
According to this rule, the diameter of a circle is equal to the sum of two radii of a given circle or two radii.
Let’s write down the formula.
D = 2R, where D is the diameter of the circle and R is its radius.
Now let’s write down and calculate.
D = 2R.
D = 2 × 4.
D = 8 (cm).
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