Circumference of a Circle Calculator
Calculate the distance around a circle using radius or diameter.
Units
Centimeters (cm)
Meters (m)
Inches (in)
Feet (ft)
Resulting Circumference:
0.00
How to Calculate Circumference of a Circle
The circumference of a circle is the linear distance around its outer edge. Think of it as the "perimeter" of the circle. To find this value, you need to understand the relationship between the radius, the diameter, and the mathematical constant Pi (π).
The Circumference Formulas
Depending on whether you have the radius (distance from the center to the edge) or the diameter (distance from edge to edge through the center), you use one of the following formulas:
Using Radius: C = 2 × π × r
Using Diameter: C = π × d
Using Diameter: C = π × d
Where:
- C = Circumference
- π (Pi) ≈ 3.14159
- r = Radius
- d = Diameter (which is 2 × r)
Step-by-Step Example
Suppose you have a circular garden with a radius of 5 meters. How do you find the circumference?
- Identify the radius: r = 5.
- Apply the formula: C = 2 × π × 5.
- Calculate: C = 10 × 3.14159.
- Result: The circumference is approximately 31.42 meters.
Why is Pi (π) used?
Pi is a unique constant that represents the ratio of any circle's circumference to its diameter. No matter how big or small the circle is, if you divide the circumference by the diameter, you will always get approximately 3.14159. This universal property makes it the core of all circular geometry calculations.
Common Conversions Table
| Radius | Diameter | Circumference (Approx) |
|---|---|---|
| 1 | 2 | 6.28 |
| 5 | 10 | 31.42 |
| 10 | 20 | 62.83 |