How Do You Find the Diameter of a Circle?

The diameter of a circle splits the circle in half. A diameter is the distance between two points on the circle's circumference, or perimeter, that passes through the circle's origin, or center. The diameter helps to define the size of the circle and is part of the calculations to find the circle's circumference and area. You can find a circle's diameter through its different properties like its circumference and area.

Things You'll Need

• Ruler
• Calculator

Instructions

1. Draw and measure a line that travels from one point on the circumference, passes through the origin and to a point on the opposite side of the circumference. This is the circle's diameter.

2. Multiply the length of the radius by 2 to calculate the diameter. The radius is the distance from the origin of the circle to the circumference. For example, a radius that measures 8 multiplied by 2 equals 16. The diameter is 16.

3. Divide the circle's circumference by pi, or π, to calculate its diameter. Pi is a lengthy mathematical constant that begins with the number 3.14. For example, a circumference of 300 divided by pi results in a diameter of 95.49.

4. Divide the circle's area by pi, find the square root of that result and then double the square root to calculate the circle's diameter. For example, the circle's area is 1,200. 1,200 divided by pi equals 381.97 and the square root of 381.97 equals 19.54, which is the radius. Double the radius to calculate the diameter. 19.54 doubled equals 39.09.

References

• Cool Math: The Geometry of Circles
• Math Goodies: Circumference
• Math Open Reference: Area Enclosed by a Circle

Resources

• CSG Network: Circle and Sphere Calculator