Circumference Calculator
Calculate the circumference of a circle from its radius or diameter using the standard formulas C = 2 pi r or C = pi d. This tool is useful for math homework, engineering projects, construction planning, and any task that requires finding the perimeter of a circular shape.
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Result
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Formula
How it works: Enter either the radius (distance from center to edge) or the diameter (distance across the circle through the center). The calculator applies the appropriate formula: C = 2 x pi x radius, or equivalently C = pi x diameter. Only one measurement is needed.
Worked Example
Frequently Asked Questions
Do I need to enter both radius and diameter?
No. Enter just one measurement. If you provide the radius, the calculator uses C = 2 pi r. If you provide the diameter, it uses C = pi d. Either value is sufficient to compute circumference.
What value of pi does the calculator use?
The calculator uses the full-precision value of pi (3.14159265358979...) built into the computing engine, giving you accuracy to many decimal places.
What is the difference between circumference and perimeter?
Circumference is the specific term for the perimeter of a circle. Both words mean the total distance around a shape, but circumference applies only to circles and ellipses.
How do I find circumference if I only know the area?
First calculate the radius from the area using r = sqrt(A / pi), then use C = 2 pi r. For example, if the area is 78.54, the radius is 5, and the circumference is 31.4159.
Can I use this for real-world measurements like pipes or wheels?
Yes. Enter the outer diameter of a pipe, wheel, or any circular object to find how far around it measures. This is commonly used in plumbing, automotive, and manufacturing contexts.
Can I use this Circumference Calculator on my own web page?
You can. Look for the "Embed" button near the top of this calculator. It lets you pick a size, border style, and color palette, then gives you an iframe tag to paste into any webpage. The widget is responsive, loads fast, and costs nothing. More details at calculory.com/services/embed-calculators.
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