Circumference Calculator
Circumference
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Area
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Radius
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Diameter
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How to Calculate Circumference
The circumference of a circle is the distance around its edge. The formula is C = 2πr (using radius) or equivalently C = πd (using diameter). Pi (π) is approximately 3.14159. This fundamental relationship means the circumference is always about 3.14 times the diameter.
This calculator also computes the area of the circle using A = πr². The area represents the total space enclosed within the circle. Both circumference and area are essential in engineering, construction, and everyday applications like determining how much fencing goes around a circular garden.
You can enter either the radius or the diameter — the calculator will compute the other automatically. All results use full precision of JavaScript's built-in Math.PI constant for maximum accuracy.
Frequently Asked Questions
What is the formula for circumference?
Circumference = 2πr or πd, where r is the radius and d is the diameter. For a circle with radius 7, the circumference is 2 × 3.14159 × 7 ≈ 43.98.
What is the difference between radius and diameter?
The radius is the distance from the center to the edge of a circle. The diameter is twice the radius — the distance across the circle through its center.
How do you find the radius from the circumference?
Rearrange the formula: r = C / (2π). Divide the circumference by 2π (approximately 6.2832) to get the radius.
Why is pi important for circles?
Pi (π ≈ 3.14159) is the ratio of any circle's circumference to its diameter. It's a mathematical constant that appears in all circle calculations.