The LessonThe circumference of a circle is found using the formula:
In the formula, d is the diameter of the circle. The image below shows what we mean by diameter:
How to Find the Circumference of a Circle
QuestionWhat is the circumference of a circle with a diameter of 10 cm, as shown below?
Start with the formula:
Circumference = πdDon't forget: π is pi (≈ 3.14) and πd = π × d.
Substitute the diameter into the formula. In our example, d = 10.
Circumference = π × 10 = 31.4 cm
Answer:The circumference of the circle with a diameter of 10 cm is 31.4 cm.
Lesson SlidesThe slider below shows another real example of how to find the circumference of a circle. Open the slider in a new tab
What Is a Circle?A circle is a shape containing a set of points that are all the same distance from a given point, its center.
Radius and DiameterThe diameter of a circle is twice the length of its radius. If you are given the radius of a circle, double it to find the diameter and put this in the formula.
What Is Pi?π is the symbol for pi. π is how many times longer a circle's circumference is than its diameter. It is the circumference divided by the diameter:
π is the same for all circles, and is approximately equal to 3.14.