That ratio is roughly three, and 3.14 is good enough for most math and science applications. 3.14159 is good enough for, like, anything. But because Pi is both infinite and patternless, people like to memorize tons of its digits to show off.
Which brings me to our first recommended Pi Day activity.
Pi Day's official Web site has a page where you can scroll through one million digits of Pi. That's a lot of Pi, guys.
If that infinite scroll isn't impressive enough for you, check out what they look like on paper: Those digits stretch out for over a mile.
3.1415 is for noobs. Celebrate your favorite math holiday at 3.1415926, like a boss. If you're waiting for an admissions decision from MIT, that's when it's going to arrive. Because nerds are cool. Also, good luck you smartypants!
It is a math holiday, after all. Phil Plait at Slate has a great collection of Pi-related facts to smarten up your day.
Here's a mathematician talking about why Pi is so impressive to him:
Nerdy though I may be, even I must admit that the main draw of March 14 is the excuse to bake and eat delicious pies. I've been known to way overprepare for the occasion, so with all the leftovers it turns into a bit of a Pi Week in my house. Which is as it should be, given the under-representation of nerd days on the federal calender.
Whether you make one pie or 3.14 of them, we've got you covered: Check out this post full of scientific pie making tips, including an explanation for why you should always put booze in your crusts. It's very important.
If you're feeling the holiday spirit, you can even purchase a pie tin shaped like the Greek symbol for Pi. Personally I think that kind of defeats the whole point, seeing as your Pi pies should be demonstrative of the principle of Pi (as seen in the video above), but what do I know.