# Circumference of a Circle Calculator

Use this calculator to easily calculate the circumference of a circle, given its radius in any metric: mm, cm, meters, km, inches, feet, yards, miles, etc.

### Calculation results

18.849556 cm Circle circumference
Share calculator:

Embed this tool!
get code

## Circumference of a circle formula

The circumference of a circle is calculated using the formula: 2 x π x radius, where π is a mathematical constant, equal to about 3.14159. It was originally defined as the ratio of a circle's circumference to its diameter (see second formula below on why) and appears in many formulas in mathematics, physics, and everyday life. In practical situations it is often easier to measure the diameter instead of the radius. If you know the diameter, it is 2 times the radius, so just divide by two, to get the radius, or use this formula: π x diameter.

The calculation result is in the unit in which you measured the circle radius or diameter.

## How to calculate the circumference of a circle?

Calculation is easy once you have measured the circle's radius or diameter, using the formulas above or, if you prefer the easier way - using our circumference of a circle calculator above. To make sure you are measuring the diameter correctly, it should be the biggest measurement you can get. If by moving the measurement instrument slightly you get a bigger diameter size, then go with that.