of a circle
is half of the diameter
How to Find the Radius from the Diameter
Finding the radius from the diameter is easy.
What is the radius of the circle, with diameter 10 cm, below?
Divide the diameter, 10 cm, by 2.
10 ÷ 2 = 5 cm
The radius of the circle is 5 cm.
The slider below shows another real example of how to find the radius of a circle from the diameter.
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to help you learn about finding the radius of a circle from its diameter.
Why Is Knowing the Radius in Terms of the Diameter Useful?
Most of the properties of a circle - such as its circumference
- can be expressed in terms of the radius or diameter.
Most students remember the area of a circle with a radius r
But what if you are told the diameter d
instead? Divide it by 2 to find the radius.
If you substitute d⁄2
, a formula for the area of a circle in terms of the diameter can be found:
Read more about how to find the area of a circle using the diameter