# Pi symbol

If you search the keypad on your calculator, you'll likely find the pi symbol

π

## What does pi mean?

Pi (pronounced pie) is the sixteenth letter of the Greek alphabet. In math, the number pi is the ratio of the circumference of a circle to its diameter

where

• π = pi
• C = circumference of circle
• d = diameter of circle

No matter what the size of the circle, the value of pi remains the same, i.e. pi is a constant.

## Use your calculator's pi symbol to take a look at the value of pi

Go ahead and press the pi symbol on your calculator (you may need to press a shift or 2nd function button to access π). The display should show

3.141592654

The digits of pi never end and don't follow a pattern. Pi's an example of an irrational number - it can't be expressed as a ratio of integers, that is to say it cannot be written as a simple fraction.

But fractions can be used to give approximate values of pi - for example

 Fraction Value Accuracy 22/7 3.142857143 2 decimal places 333/106 3.141509434 4 decimal places 355/113 3.14159292 6 decimal places

## What's pi used for?

You already know pi's used in calculating the diameter and circumference of a circle.

Other applications include working out a circle's radius and area, and the volumes and surface areas of cylinders, cones and spheres.

In other words, pi is extremely useful when performing two and three dimensional shape calculations!

## A fun way to memorize pi!

Computers have been used to calculate pi to millions of decimal places.

Fortunately, you don't need to remember many of the digits of pi, although some people practice the discipline of piphilology to help them recall pi's value.

Try the following mnemonic

How I wish I could recollect pi easily today!

Notice how the number of letters in each word represents a digit in the pi number sequence. This mnemonic helps you memorize pi to 8 decimal places, i.e. 3.14159265.

Of course you can use your calculator but there are a couple of other neat ways of remembering that pi approximates to 3.14 or 22/7.

National Pi Day is celebrated in the United States annually and is held on 14 March i.e. 3/14!

Also Pi Approximation Day is observed on 22 July i.e. 22/7!

Why not hold your own celebrations?

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