Circumference Calculator
Compute the distance around a circle: C = 2 × π × r.
Calculator
Use the Circumference Calculator
Result
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Formula
C = 2 × π × r
Step-by-step
- 1
Enter the radius
Distance from center to edge.
- 2
Read the circumference
Perimeter of the circle.
Worked example
Example input: a: 5
Result: 31.4159
Related tools
- Circle Area
π × r².
Frequently asked questions
What is the circumference formula?
C = 2πr when you know the radius, or C = πd when you know the diameter. A radius of 5 units wraps around to about 31.42 units; enter any radius above and π is applied automatically. Both forms agree, since 2πr and πd describe the identical number with d = 2r substituted.
How is circumference different from area?
Circumference measures the distance around the circle and comes out in plain units; area measures the surface inside and comes out in square units. The same circle with r = 5 has circumference 31.42 units but area 78.54 square units.
Which value of π does the calculator use?
The built-in constant Math.PI ≈ 3.14159265. The precision is far beyond what any physical circle can be measured, so rounding the final answer to 2 decimals is purely for presentation.