Circumference Calculator — Calculate Circle Perimeter
Calculate the circumference (perimeter) of a circle from its radius or diameter. See also Area of Circle Calculator and Arc Length Calculator.
How to Calculate Circumference
1. Measure the radius (distance from center to edge) or diameter (distance across the circle through the center). 2. If using radius, multiply by 2 and then by pi (3.14159). 3. If using diameter, multiply directly by pi. 4. The result is the circumference — the total distance around the circle.
Circumference Formula
C = 2 x pi x r (using radius)
C = pi x d (using diameter)
Area = pi x r^2
Where pi = 3.14159265...
Example
Find the circumference of a circle with radius 5 cm:
C = 2 x pi x r
C = 2 x 3.14159 x 5
C = 31.4159 cm
Circumference Reference Table
| Radius | Circumference | Area |
|---|---|---|
| 1 | 6.2832 | 3.1416 |
| 2 | 12.5664 | 12.5664 |
| 3 | 18.8496 | 28.2743 |
| 4 | 25.1327 | 50.2655 |
| 5 | 31.4159 | 78.5398 |
| 6 | 37.6991 | 113.0973 |
| 7 | 43.9823 | 153.9380 |
| 8 | 50.2655 | 201.0619 |
| 9 | 56.5487 | 254.4690 |
| 10 | 62.8319 | 314.1593 |
Frequently Asked Questions
What is circumference?
Circumference is the distance around the outside of a circle, also called the perimeter of a circle. It is calculated using C = 2 x pi x r or C = pi x d.
What is the difference between circumference and perimeter?
Circumference specifically refers to the perimeter of a circle. Perimeter is a general term for the distance around any shape, while circumference is used exclusively for circles.
How do I find circumference from area?
First find the radius: r = sqrt(A / pi). Then calculate circumference: C = 2 x pi x r. For example, if area = 78.54, then r = 5 and C = 31.42.
What is the circumference of a circle with diameter 10?
C = pi x d = 3.14159 x 10 = 31.4159 units. The circumference is always pi times the diameter.
Why is pi used in circumference calculations?
Pi (3.14159...) is the ratio of any circle's circumference to its diameter. This ratio is constant for all circles regardless of size, making it fundamental to all circle calculations.