Use our Circumference Calculator to determine the circumference of a circle.
Does calculating circumference have you running in circles? Our circumference calculator is an easy way for you to find the circumference of any circular object. Simply enter the radius of the circle and hit “calculate.” You can click the “reset” button if you need to clear the circumference calculator in order to find the answer for another circle.
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And if you're not sure what the radius is or how to find it, we'll walk you through some of the basics of finding a circle's circumference below.
What is the Circumference of a Circle?
The circumference of a circle is the measurement around a circle's edge. It can be compared to finding the perimeter of a shape (although the word perimeter is reserved specifically for polygons). If you were to cut a circle and lay the outline flat, the length of the line it created would be its circumference. The circumference can be measured in any unit or system that traditionally measures length - imperial (inches, feet, etc.) or metric (centimeters, meters, etc.). Whichever unit the radius is measured in will also be the unit the circumference is calculated in.
The equation used to find circumference is C = 2Πr, where C stands for circumference, R stands for radius, and Π is Pi, a mathematical constant equivalent to approximately 3.14 (see more below).
You can also calculate the circumference of a circle using the diameter, with the equation C = Π * d. If you only have the diameter of a circle and would still like to use this calculator, you can find the radius by dividing the diameter in half.
We suggest working out some problems on your own and using the calculator to check your answer, as it provides you with a solution for each problem but will not show you the work that goes with it.
Parts of a Circle
- Circumference: The distance once around the circle. It can also be understood as the circle's perimeter.
- Radius: The distance from the center of the circle to its edge. No matter which direction you measure in, the radius will be the same from any point on the edge of the circle.
- Diameter: A straight line across the circle that intersects through the center point. This measurement is always equal to twice the radius (2r).
The Value of Pi
Pi (Π) is a non-terminating number, which means it goes on forever and has no end. Its value is about 3.1415926535897... Pi is also a constant, which means it is always equal to the same value.
The Greek letter p (pronounced as "pie") is used to describe this number. It stands for the ratio between the circumference of any circle and its diameter, and it's true for all circles. This means that any circle’s circumference will be about 3.14 times the length of its diameter.
Circumference Equation Example
What is the circumference of a circle whose radius is 24 inches?
Circumference = 2×Π×r
C = 2 × 3.14 × 24
C = 150.79 inches
When you enter the radius of 24 into our calculator, it provides you with an answer of 150.79644737231007, which is a more precise answer. This is because it uses a more accurate number for Pi, rather than rounding to 3.14.
Our circumference calculator provides circumference of a circle by entering its radius. Our circumference calculator is free to use any time you want to determine the circumference of a circle!
We also have a fun instructional video on diameter, radius and circumference of a circle right here: Circumference of a Circle Video .