National Pi Day is recognized today in the U.S. and around the world. Here's what to know about the quirky holiday, and how to celebrate.

What is pi? Pi can calculate the circumference of a circle by measuring the diameter — the distance straight across the circle’s middle — and multiplying that by the 3.14-plus number.

Scientists have calculated pi to 105 trillion digits, although most of us are more familiar with the approximation 3.14. But how do we know that pi is an irrational number?

Indiana once tried to define pi digits as 3.2; bill almost passed before Purdue professor stepped in What is pi? Irrational number famously extends without repeating ...

Pi, which is the ratio of a circle's circumference to its diameter, is celebrated with its own holiday on March 14.

What is Pi Day, and why do we celebrate it every March 14? Here's what to know as math lovers around the world mark Pi Day.

Pi Day is a favorite holiday for both food lovers and mathematicians. For the foodies, the reasoning is simple. Pi Day brings discounts and deals for people looking to grab a pizza to celebrate ...

What is Pi Day, and why do we celebrate it every March 14? Here's what to know as math lovers around the world mark Pi Day.