How to Calculate Circumference in Inches

••• wathanyu/iStock/GettyImages

One way to measure a circle's circumference in inches is to measure around the circle, but all that bending might break your ruler. A simpler way is to take advantage of circular properties, like the math constant pi. Pi, also known as π, is one of the most important constants. A ratio of a circle's circumference to its diameter, pi never terminates but is often given as just 3.142. You can calculate the circle's circumference in inches with pi in the equations circumference = 2 * radius * pi and circumference = diameter * pi.

    Locate the circle's center, and measure the length from its center to a point on its edge to find the radius. For an example, suppose the measurement is 5 inches.

    Double the length to calculate the circle's diameter. For this example, multiplying the length of 5 inches by 2 results in 10 inches.

    Multiply the measurement calculated in the previous step by pi. To conclude this example, multiplying 10 by pi results in 31.42. The circle's circumference is 31.42 inches.

    Things You'll Need

    • Ruler
    • Calculator


    • Alternatively, you can measure a straight line that travels between two points on the circle's circumference and passes through its center to obtain the diameter and skip to Step 3.

Related Articles

How to Calculate a Spiral
How to Find the Volume of a Sphere in Terms of Pi
How to Calculate the Volume and Circumference of a...
How to Calculate the Diameter of a Circle From a Linear...
How to Solve a Hexagon
How to Calculate the Area of a Curved Surface
How to Calculate a Circular Area
How to Calculate Volume of a Circular Cylinder
How to Find the Perimeter of Different Shapes
Differences Between Circumference & Diameter
How to Find the Circumference of an Octagon
How to Calculate Cubic Inches in a Cylinder
How to Figure the Cubic Yards in a Circle
How to Find the Radius of a Circle
How to Calculate the Area & Circumference of a Circle
How to Calculate the Linear Footage in a Radius
How to Calculate Volume of a Rectangular Prism
How to Convert 55 X 40 X 20 CM to Inches
How to Find the Height of a Rectangular Pyramid
How to Find the Radius of a Sphere When Given the Volume