“Pi Day” has become a popular math day, and people around the world celebrate this special day each year on March 14. Read on to find out why this date has been matched with pi.

Pi is actually a letter from the Greek alphabet, and is usually written with its symbol, π. It is one of several Greek letters used in math to represent special numbers. In pi’s case, using the letter is much easier than writing the actual number.

In math, π stands for the ratio of the circumference (distance around) compared to the diameter (distance through the center) of a circle. No matter the size of a circle, the ratio is always the same.

Finding Pi

Discover pi for yourself with an experiment using a variety of household objects.

Measurement Tool

• measuring tape, if available
• string or ribbon
•  

Objects

• at least four items with a circular end
• examples: food cans, drinking glasses, or mugs

The Experiment

1. With your measuring tool, measure the distance around one of your circular objects and note the total length.

• If using a measuring tape, write the measurement on paper.
• If using a string or ribbon, mark the string with a marker, paper clip, or knot to show the measurement on the string itself.

2. Measure straight across the middle of the circle. You will know you’re in the middle when you get the longest measurement.

• If using a measuring tape, divide this number into your first number and note the quotient. You can write any remainder as a fraction.
• If using a string or ribbon, see how many times you can measure across the circle before you get to the mark. Keep notes on paper.

3. Repeat the experiment until you have measured all of your objects.

Calculating Pi

You should have found that the distance around each circular object was a little more than three times the distance straight across. In some cases, this estimate is all that is needed. At other times, you may need to be more precise.

If you use whole numbers and conduct your experiment enough times, you will find that the value will be pretty close to  .

If you use decimals, your answer will depend on how precise your measurements are. You may find that your answer is a simple decimal around 3.2, or you may find that the division never ends because you always have a remainder. The decimal that is equal to

the bar over the decimal part means that the division will keep repeating those six digits in that pattern without ever ending.

The actual process for calculating pi requires advanced mathematical processes. The result is a decimal that never ends and never repeats in a pattern. The first ten digits in the decimal part of pi are: 3.1415926535.

Conduct a safe search on the Internet to see the actual value of pi calculated to hundreds, even millions, of decimal places. You’ll be amazed what you find.

Breaking a Record with Pi

Throughout history, people have taken on the challenge of computing pi to as many decimal places as possible. The current world record is ten trillion digits, set in August 2011. Keep in mind that a trillion is a million millions!

Other people have turned the challenge of memorizing pi’s digits into a sport. The current record-holder was able to recite 70,000 digits of pi in March 2015!

Celebrating Pi

Have you figured out why March 14 is celebrated as Pi Day? March is the third month, and the day could be written 3.14. In 2016, Pi Day was extra special because the date written with the year fit the pattern of pi digits as well: 3.14.16!

What better way to celebrate pi than to eat pie! It’s as good an excuse as any to enjoy a delicious treat, especially when that treat is round!

While enjoying your favorite pi(e), explore pi in art, music, poetry, literature, and nature.