GeometryFree

Radius to Circumference Calculator

Calculate the circumference of a circle when you know the radius, using the formula C = 2 pi r. Enter the radius in any unit and get the circumference instantly. This is the standard geometry formula taught in school and used in engineering, architecture, and manufacturing.

Enter Values

Radius

Result

Enter values above and click Calculate to see your result.

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Formula

Core Formula

C = 2\pi r

How it works: Multiply the radius by 2 and then by pi (approximately 3.14159). The radius is the distance from the center of the circle to any point on its edge. Doubling the radius gives the diameter, and multiplying by pi converts it to the full distance around.

Worked Example

A circle with radius 7 cm: C = 2 x pi x 7 = 14 x 3.14159 = 43.9823 cm. If this were a wheel, one full rotation would cover approximately 44 cm of ground.

Frequently Asked Questions

Is the radius half of the diameter?

Yes. The radius is exactly half the diameter. If you know the diameter, divide by 2 to get the radius. Conversely, double the radius to get the diameter.

Can I reverse this calculation to find radius from circumference?

Yes. Divide the circumference by 2 pi (approximately 6.28318) to get the radius. The formula is r = C / (2 pi).

What real-world applications use radius to circumference?

Calculating how much fencing is needed around a circular garden, finding the distance a wheel covers per rotation, sizing belts for pulleys, and determining the perimeter of circular pools or tanks.

Does the unit of radius matter?

The circumference will be in the same unit as the radius you enter. If you enter radius in centimeters, the circumference is in centimeters. If in inches, the result is in inches.

Is it possible to embed the Radius to Circumference Calculator on another website?

Yes, embedding the Radius to Circumference Calculator is free. Hit the "Embed" button on this page, adjust the width, height, and theme, then grab the iframe code. It works on WordPress, Wix, Squarespace, Shopify, and plain HTML pages. No registration needed. Full instructions at calculory.com/services/embed-calculators.

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