Finding the Diameter from the Circumference
(KS3, Year 7)
The LessonThe diameter of a circle is found from the circumference of a circle using the formula:
In this formula, C is the circumference of the circle. The image below shows what we mean by finding the diameter from the circumference:
How to Find the Diameter from the CircumferenceFinding the diameter from the circumference is easy.
QuestionWhat is the diameter of the circle, with circumference 30 cm, below?
Start with the formula:
Diameter = C⁄πDon't forget: / means ÷ and π is pi (≈ 3.14)
Substitute the circumference into the formula. In our example, C = 30.
Diameter = 30⁄π Diameter = 30 ÷ π Diameter = 30 ÷ 3.14 Diameter = 9.6 cm
Answer:The diameter of the circle is 9.6 cm.
Lesson SlidesThe slider below shows another real example of how to find the diameter of a circle from the circumference. Open the slider in a new tab
Interactive WidgetHere is an interactive widget to help you learn about finding the diameter of a circle from its circumference.
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