The LessonThe circumference of a circle is found using the formula:
In the formula, r is the radius of the circle. The image below shows what we mean by radius:
How to Find the Circumference of a Circle Using the Radius
QuestionWhat is the circumference of a circle with a radius of 5 cm, as shown below?
Start with the formula:
Circumference = 2πrDon't forget: π is pi (≈ 3.14) and 2πr = 2 × π × r.
Substitute the radius into the formula. In our example, r = 5.
Circumference = 2 × π × 5 = 31.4 cm
Answer:The circumference of the circle with a radius of 5 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.
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.