Pi (π) Day is celebrated on March 14th in the US. It’s mainly celebrated by students, teachers and professors, lovers of math, and mathematicians.

In case you forgot… What is Pi Again?

Pi (π) is the ratio of a circle’s circumference to its diameter. To break it down into a simple formula:

π = circumference of a circle/its diameter

The circumference is the distance around the circle. The diameter is the distance from one side of the circle to the other, if you drew a line that passes through the center of the circle.

Pi is particularly useful when you’re trying to work out the area of a circle or an arc.

One important thing about pi is that it’s always the same no matter how big or how little the circle is. This makes sense – because a circle is always a circle – no matter how big or small it is – the ratio of its circumference to its diameter is always the same – it’s pi!

Pi = 3.14159265358979323846264338327950288419…

The … means that the number goes on an infinite amount.

The amazing thing about pi is that it’s an irrational number. Yet it’s still useful in our day to day life. Like if we wanted to figure out the area of a circular rug, you’d need to use pi. Go figure!

Why is Pi Celebrated on this Day?

March 14th is Pi Day in the US. That’s because in the US, you write March 14th as 3/14. So if you figure…

Pi = 3.141592653589793238462643383279502…

The 3.14 is where you get the 3/14 for March 14th. (To make this date even more propitious, Albert Einstein was born on March 14th in 1879.)

Of course, you’re talking about mathematicians, so figuring out what time to celebrate Pi Day isn’t simple.

Most people would say the correct time to celebrate it is at 1:59, since those are the numbers in pi that come after 3.14. There’s a debate about whether it should be am or pm. I assume college students would chose to celebrate Pi Day at 1:59 am for its accuracy (plus they can stay up to have a party in the middle of the night). Presumably most high school and middle school kids would be more likely to celebrate Pi Day at 1:59 pm. Though I must warn you that some people celebrate it at 3:14!

In Europe and other parts of the world, Pi Day is celebrated on January 3 at 4:15. That’s because they would write the date putting the number for the day first (3) and then the number for the month (1). So they’d write the date as 3/1 then add the time 4:15 and you get some of the numbers in pi: 3.1415…

Why is Pi Called Pi?

π is the Greek letter for P. π is also the first letter of the Greek word for periphery (or circumference).

How Can You Celebrate Pi?

Here are some ideas:

-Eat pizza pie on pi day.
-Make a pie with a pi sign on it to eat.
-Have a contest to see who can remember the most digits in the number pi. Perhaps the winner can win a pineapple.
-Have a pie throwing contest!
-Sing Pi Day Carols.
-Prove that π = 3.14…

Idea for Teaching Pi or How to Show that π = 3.14159…

I think this is a wonderful hands-on experiment to help children understand why π = 3.1415… The gist of this experiment is to take different sized jar caps and have the children measure them. 1st they will cut a piece of string to get a measurement for the circumference. Then they will cut another piece of string to get a measurement for the diameter. Then they measure each string. Then they work out how many “diameter” strings they will need to get a measurement for the length of the “circumference” string. The answer should be in decimals. The class should take all of its data and average it out. The answer should be close to pi.

For full instructions of this experiment go to What is Pi? A “Cool” Lesson

There’s also a cool one-page pi poster you can print out for your child or students.

Many thanks to Calvin for pointing out this holiday to me!

Happy Pi Day to You All!

Lisa