**In this module, you can study ****how to calculate the distance around a circle (its circumference) if you know its diameter.**

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**Pi **is the name for a very long number: 3.1415926535897932384626433832795028841971...

**The symbol for ****pi** is: π

A scientific calculator has a button 'π' to press if you need to use pi.

**Formula for calculating a circle's circumference: **2πr

This means: 2 x 3.14...(π) x radius length

**Study and practice**

- Try your hand at changing a circumferenceDrag the radius of this circle to resize it and watch what happens to the circle's circumference (called perimeter in this example).
- Study how to find the circumference of a circleThis online lesson provides a good explanation about how to use either radius or diameter to calculate the circumference of a circle.
- Download a worksheet for area and circumference of a circleLink to math-aids.com to create your own worksheets for studying area and circumference of a circle. Answers included.
- Quiz yourself on finding circumferencesThis site provides a circle's radius or diameter and asks you to calculate the circumference.

The video explains how to use the pi button on a Casio fx-991 scientific calculator to calculate the circumference of a circle.

- Online scientific calculator from Calculator.netTo open the scientific calculator in a new window, you MUST click the link.