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

Circle circumference 18.849556 cm
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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.

circumference circle

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.

Practical application

Circles are often used in by architects for athletic tracks, recreational areas, buildings, and roundabouts. The famous Ferris-wheel is a circle. Circle-like parts, e.g. cylinders, tubes, gears, and others are used by engineers for making clocks, bikes, cars, trains, ships, planes, and even rockets. The invention of the wheel-cart was one of the transforming events in early human history. The number π has application in calculating important statistical distributions like the normal distribution (gaussian distribution).

Cite this calculator & page

If you'd like to cite this online calculator resource and information as provided on the page, you can use the following citation:
Georgiev G.Z., "Circumference of a Circle Calculator", [online] Available at: URL [Accessed Date: 24 Mar, 2019].