Circle Circumference Calculator

Find the distance around a circle from its radius. The circumference is a length, so a radius in cm gives a circumference in cm.

How to use Circle Circumference Calculator

1. Choose Measurement Unit, then enter Radius without a unit suffix. 2. Use the selected ordinary, square or cubic unit for each measurement as explained below; changing the selector relabels inputs and does not convert them. 3. Select Calculate, or press Enter, and read circle circumference. 4. Select Select Copy result to copy the answer, or Reset to clear the form.

Why use this tool?

Estimate edging, trim or the distance around a circular item before adding joins or fitting allowances.

How the calculation works

Circumference = 2 × π × radius. Equivalently, circumference = π × diameter. Results use up to six decimal places. Tiny nonzero results below 0.000001 use scientific notation with six significant digits. Browser floating-point arithmetic can introduce small rounding differences. Inputs and calculated magnitudes must not exceed 9,007,199,254,740,991. Negative physical measurements and arithmetic underflow are rejected. Zero dimensions are treated as a degenerate limit where the formula allows them; divisors and sides of an actual triangle must be positive. Formula reference: https://openstax.org/books/prealgebra-2e/pages/c-geometric-formulas

Example

Radius = 5 cm gives 2 × π × 5 = 31.415927 cm.

Practical tip

Measure from the centre to the edge for the radius. Add any overlap required by your material separately.