**Each year March 14 is a U.S. annual celebration of Pi Day**. Many outside the States also join in on the festivities. Math geeks usually engorge themselves with some type of pie or Greek food while having discussions about—you guessed it—**pi**. Albert Einstein was born on **Pi Day**. So you’re among some great minds as you contemplate this date. If you are not planning two to four weeks ahead, there’s a chance your **pi** party may be more irrational than the number.

## Rationale Behind the Irrational Pi

**Pi** (π) is the 16th letter of the Greek alphabet. It is used to represent the numeric constant associated with the ratio between the diameter and circumference of a circle. Take any circle, regardless of size, and *divide* the circumference by the diameter (distance across center) and you will end up with **pi**. Likely more useful, you can *multiply* the diameter by **pi** to find out the circumference.

To approximate how many ** steps** it takes to walk around a perfectly round track, walk straight across the middle. Then multiply your steps times

**pi**. You can also approximate the

**it takes to walk around the track by multiplying the duration of walking straight across the diameter by**

*time***pi**.

Multiply circle diameter by Pi to find out the circumference.

**Pi** is a mathematical constant representing an irrational ratio. This means it has infinite digits to the right of the decimal that lack any repeating patterns. Nicholas Sze calculated the 2 quadrillionth digit of **pi**. It took 23 days on 1,000 of Yahoo’s advanced computers. On a standard PC, the calculation would have taken 500 years. Powerful computers have so far sequentially identified the first 12.1 trillion digits of **p****i**. You can view 10,000 digits on CNN.

Want more **Pi Day** madness? To find out the perimeter of a square, simply multiply the length of a side by 4. If you center an overlapping a circle of equal width, there is how much space in each corner? Subtracting **pi** from 4 equals 0.86. Divide this by 4 to reveal that each of those semi-triangles is 0.215 percent of the square perimeter. If you bake a square cake that is 9.132 inches wide (w) and you cut it into a perfect circle with an equal diameter, you will have wasted 10 **pi**s (w*4*0.86). Multiply by the cake thickness for volume.

## Remember My Favorite Pi

You can strive to memorize at least the first 10 decimal digits of **pi**. This will keep you from staring like a deer in the headlights during water cooler **pi** conversations. It also allows you to say something other than “Nerd!” when someone mentions **Pi Day**. And we *know* the weekend talk will include the question: “What did you do for **Pi Day**?”

Nicholas Sze, of tech firm Yahoo, said that when

piis expressed in binary, the two quadrillionth “bit” is 0.

People devise many ways to recite long strings of **pi** from memory. Savants with synesthesia may view the numbers as colors. Others visualize scenes within 3D worlds where different numbers of items appear within a room. You might try to find obtuse logic to the irrational pattern in the example below.

The first four digits right of the decimal point are 3.**14****15**. Recall the next three digits as a set; the “9” is transposed “2” a “6.” This brings us to 3.**1415****926**. Conclude with “5–35.” So **pi** with ten digits is 3.**1415926****535**. Want to retain four more decimal places? Add together the last two digits for “8,” which is often rounded up to “9” since the following three digits are "979." Wow, you’re already up to 14 digits: 3.**1415926535****8979**…

## Pi Day Fun and Games

Congratulations! When you go out to eat your favorite pie with three other friends on the 14th, recite successive **pi** decimals around the table. Since there’s 3+1 of you, three can pay 31.4 percent. Let the designated driver pay the remaining 0.58 percent. (You *are* driving, right? Plan ahead while sounding spontaneous.) For more of a challenge regardless of group size, let the person who can’t name the next digit pay the entire tab. The National Council of Teachers of Mathematics has a page with numerous activities and resources.

We have a couple pizza pie and Greek Pi themed lapel pins. Because the demand is only once per year, inventory is limited. Order early! What are your plans for the next **Pi Day**?

If you’re not inspired to bake a pie, here’s a Kraft recipe you can prepare in 10 minutes with no baking. It takes more effort to drive to a local bakery (if you remembered to order in advance). If it is too crowded to go out for pizza, ClinicalPosters has a Pinterest board that may inspire you to warm up the oven.