Circle Length Calculator

Created by Luis Hoyos
Reviewed by Wojciech Sas, PhD
Last updated: Sep 25, 2022

If you want to learn how to calculate the length of a circle, our circle length calculator is the perfect tool 🎯. You can use this calculator to:

  • Find the length of the radius of the circle.
  • Calculate the length of the diameter of a circle.
  • Find the length of the circumference.

Read on to learn more about how to find the length of a circle.

Radius, diameter, and circumference: the circle length formula

Radius r, diameter d, and circumference c are related. The higher the radius or the diameter, the higher the circumference. The circle length formula connects these variables in a single equation:

c = 2πr

If you only know the diameter, you can find the length of the radius of the circle by simply remembering the diameter is twice the radius:

r = d/2

Reordering the equations, you can also calculate the length of the circle diameter in terms of the circumference:

d = c/π

Similarly, you can know what the length of the radius of the circle is:

r = c/(2π)

How to calculate the length of a circle?

Let's suppose you want to know what is the length of the radius of a circle of 10 cm circumference. You can follow these steps:

  1. Use an adequate formula to solve your problem. In this case, it would be r = c/(2π).
  2. Input the circumference in the formula. The result should be: r = 10cm / (2π).
  3. Double-check your results. Input 10 cm in the circumference box of the circle length calculator. The result should also be 1.59155 cm for the radius.


What is the length of half a circle?

The length of half a circle is π (pi) times radius, expressed with the formula as chalf = πr or chalf = πd/2. It is the length of an ordinary circle divided by two in this case.

What is the circumference of a 6-inch circle?

18.8496 inches. To find the circumference of any circle, multiply its diameter by π. In this instance:

  1. Take the circle's diameter, which is 6 in.
  2. Multiply it by π.
  3. The result is 18.8496 in.
Luis Hoyos
Image of a circle with radius, diameter, circumference and area marked.
Radius (r)
Diameter (d)
Circumference (c)
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