How to Calculate the Circumference of a Circle

Circles are tricky shapes when it comes to measuring. Unlike a square, you cannot find the length of the outside of a circle by measuring its edges. The length around a circle is known as circumference. Unless you have a flexible tape measure, finding the circumference is going to require some basic mathematical skills and the use of a simple math formula. Here are the steps to calculate the circumference of a circle.

Things You'll Need

• Ruler

Instructions

1. Determine the diameter of the circle. This is a line drawn from one edge of the circle to the other, passing through the center of the circle. Measure the diameter if it is not given to you in the problem.

2. Learn the formula for circumference. This formula is C = pi * d. In this formula the C stands for circumference and d stands for diameter.

3. Use 3.14 or 22/7 for pi, depending on whether or not you have a fraction in your measurement. Remember that pi is a number that never ends, but 3.14 is a good estimate.

4. Calculate the circumference by doubling the radius, if you are given the radius of the circle instead of the diameter. This formula is C = pi * 2r, where r stands for the radius.