What is the Circumference to Diameter Calculator?
This tool converts the distance around a circle (its circumference) into the distance straight across it (its diameter). Because every circle shares the same constant ratio between these two measurements, the conversion is a single, exact division. Enter any circumference value — in centimeters, inches, meters, or any unit you like — and the calculator returns the diameter and radius in the same unit.
How to use it
Type the circumference of your circle into the input box and submit. The result panel shows the diameter as the headline figure, plus the radius (half the diameter) for convenience. Since the formula is unit-agnostic, the output uses whatever unit you entered.
The formula explained
The circumference of a circle is defined as \(C = \pi \times d\), where \(\pi\) (pi) \(\approx 3.14159\). Rearranging for the diameter gives $$d = \frac{C}{\pi}$$ The radius is simply \(r = \frac{d}{2} = \frac{C}{2\pi}\). Pi is a fixed mathematical constant, so the relationship holds for every circle no matter its size.
Worked example
Suppose a circular table has a circumference of 31.4159 cm. Dividing by \(\pi\): $$d = \frac{31.4159}{3.14159} \approx 10 \text{ cm}$$ The radius is therefore 5 cm. A measured circumference of 100 inches would give a diameter of \(\frac{100}{3.14159} \approx 31.83\) inches.
FAQ
Does the unit matter? No. The diameter comes out in the same unit as the circumference you entered, since \(\pi\) is dimensionless.
How do I get the radius instead? The radius is half the diameter, or \(\frac{C}{2\pi}\). The calculator shows it automatically.
Is the answer exact? The formula is exact, but \(\pi\) is irrational, so results are rounded for display. Use more decimals for high-precision work.
