# Pi Day: 5 things you need to know about this very special 3.14

It comes but once a year, and math geeks circle it on their calendars. Pi Day is celebrated every year around the world on March 14. What else do you need to know? So glad you asked.

*Here are five things you need to know about Pi Day (your friends will be impressed):*

**1. It's circumference over diameter.**

What the heck is pi, and that crazy symbol people use to describe it? Don't call your math-loving friends and beg them to explain it (mostly because they'll mock you endlessly for not knowing already). We like you, so we'll tell you.

Answer. It's the ratio of the circumference of a circle to its diameter, which is approximately 3.14159. Pi is a constant number, which means that for all circles of any size, pi will be the same.

**2. It lasts forever.**

We know that's not true about most things, but pi-- well, consider it an exception. The Bible famously set its value at 3, but it has been calculated to over a TRILLION digits beyond it's decimal point. Fortunately, you only need a few of those digit for most typical calculations.

PHEW.

**3. You'll (probably) never see a Pi Day like this again. We promise.**

This Pi Day is unlike most. Why? It's considered 'perfect' because THIS time, it's 3/14/15... and since pi really has an infinite number of digits beyond the decimal point, starting with 3.141592653, only ONCE A CENTURY is it ever actually 3/14/15 at 9:26:53 (well, twice, if you count am and pm). So unless you're around in 2115... well, this is your one shot to say been there, done that (and yes, you can even get the t-shirt).

Got it?

**4. MIT hopefuls are stalking it.**

For students hoping to attend the Massachusetts Institute of Technology, it'll be a REALLY important day. For the last few years, MIT has offered their admissions decisions online on Pi Day. So you can bet they'll be paying attention to their email at 9:26 a.m.

**5. Pi and PIE are two different things.**

But that doesn't mean you can't celebrate Pi Day with FOOD-- and your social media buddies (at least one or two) are probably guaranteed to do it, too. Get ready for a flood of pie pics with the Greek letter that stands for pi baked in the middle to basically eat up your Instagram. #piday

Pass the apple and don't be stingy on the ice cream, please. Pizza fans, you're covered too. In fact, the Washington Post put together a fabulous list of all the places you can celebrate Pi Day around D.C. (hint: Baked and Wired, Pizza Paradiso, and a whole lot of $3.14 price tags for the win!) Check it out here.

So now that you're educated, what are you waiting for? Get out there and celebrate the 'perfect' Pi Day!

**More info: piday.org**