Some 4,000 years ago, Babylonian and Egyptian scholars calculated the ratio of a circle's circumference to its diameter—or π—to be 3.125 and 3.1605, respectively. Archimedes later refined their estimations to 3.14163. Today, with the help of computers, scientists have calculated some 10 trillion digits of pi. In our celebration of Pi Day (March 14, or 3.14), mathematician Steven Strogatz talks about how the ancients calculated pi—and how you can do it at home with a box of toothpicks.