What Is the Circumference of a Cylinder?
A cylinder has a circular cross-section, and its circumference is simply the distance around that circular base (or top). Because both ends of a right cylinder are identical circles, the circumference of a cylinder equals the circumference of its base circle. This calculator finds that value from either the radius or the diameter.
How to Use This Calculator
Choose whether you are entering the radius or the diameter of the cylinder, then type the measurement in any consistent unit (cm, inches, meters, etc.). The calculator returns the circumference along with the radius and diameter so you can double-check your input. The result is in the same unit you entered.
The Formula Explained
The circumference of a circle is given by \(C = 2\pi r\), where \(r\) is the radius and \(\pi \approx 3.14159\). Since the diameter \(d\) is twice the radius (\(d = 2r\)), the same formula can be written as \(C = \pi d\). For a cylinder, this is the perimeter of the circular face — useful for wrapping labels, calculating belt or band lengths, and surface-area work.
Worked Example
Suppose a cylinder has a radius of 5 cm. Then $$C = 2 \times \pi \times 5 = 10\pi \approx 31.42 \text{ cm}.$$ If instead you knew the diameter was 10 cm, $$C = \pi \times 10 = 10\pi \approx 31.42 \text{ cm}$$ — the same answer, as expected.
FAQ
Does the height of the cylinder matter? No. The circumference only depends on the circular base, so the cylinder's height does not affect it.
What units does the result use? The circumference is returned in the same unit you entered for the radius or diameter.
How do I find the radius from the circumference? Rearrange the formula: \(r = C / (2\pi)\).
