Circle Circumference Calculator

Work out circle circumference instantly with clear inputs, formula shown and shareable results.

About Circle Circumference Calculator

Every circle has the same ratio of circumference to diameter, namely π. So C = πd = 2πr, and the enclosed area is πr².

Formulas

Circumference

C = 2πr = πd

Area

A = πr²

Worked example

With the default values below, Circle Circumference Calculator returns Circumference of 31.4159. Change any input above and every figure here is recalculated in your browser.

Inputs used

Radiusminimum 0: 5
Number of lapsminimum 0: 1

Results

Circumference: 31.4159
Diameter: 10.0000
Area: 78.5398
Distance over all laps: 31.4159

Step by step

1Values used
2Circumference
3Area
4Circumference= 31.4159
5Diameter= 10.0000
6Area= 78.5398
7Distance over all laps= 31.4159

Assumptions and limits

The result is derived only from the 2 inputs listed above. Anything not among them is not part of the calculation.
In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
Figures are rounded for display to 4 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Frequently Asked Questions

Circumference for radius 5?

2π × 5 = 10π ≈ 31.415927 units.

Why is π irrational?

It cannot be written as a ratio of integers; Lambert proved this in 1761, and it is also transcendental.