# Pi Day

**Pi Day** is an unofficial holiday that celebrates the mathematical constant pi (π). It is celebrated on March 14 in countries that follow the month/day date format because the digits in this date (3/14) correspond with the first three digits of π (3.14).

In countries that follow the day/month date format, the holiday comes few months later on July 22 and is called **Pi Approximation Day**. This is because July 22 or 22/7 is the approximate value of π (22/7 = 3.14).

Pi Day on March 14 also coincides with Albert Einstein’s birthday.

## An Ancient and Universal Constant

Pi (π) is one of the oldest, widely known and one of the most recognized mathematical constant. It is the ratio of any circle’s circumference to its diameter in Euclidean space or the ratio of a circle’s area to the square of its radius. The value of pi is approximately equal to 3.14159265, but it is an irrational number and its decimal representation never ends or repeats.

The lower case Greek letter π is used to denote the constant because it is the first letter of the Greek work περίμετρος, meaning perimeter.

## Celebrating Pi Day

Pi Day was founded by Larry Shaw and celebrated for the first time in 1988 at the San Francisco Exploratorium. Public and museum staff marched around a circular space and ate fruit pies.

Students, mathematicians and math enthusiasts all around the world celebrate Pi Day by participating in pi themed activities and contests that include making and eating pies, converting numbers such as the time or one's age using pi, and reciting the digits of pi.

Need more ideas to celebrate this awesome holiday? What about wearing a t-shirt that has the numbers of pi on it or some pi shaped accessories? Eat foods that start with a pi, like pineapples and pizza or foods that are circular in shape like pancakes and cookies; watch the 1998 Darren Aronofsky movie, Pi; make pies in the shape of pies; or attend a Pi Day event at your local school, university or museum.

In 2015, Pi Day (3/14/15) had a special significance. This year, the digits of the date 3/14/15 corresponded to the first 5 digits of pi: 3.1415. In addition, at 9:26:53 am and 9:26:53 pm on March 14, 2015, the date and the time exactly corresponded to the first 10 digits of pi: 3.141592653. Many people called this the **Pi Second**. This only happens once in a century!

Jeffrey S. Rosenthal, a professor of Statistics at the University of Toronto had also suggested the designation of the Pi Instant - the exact instant at which the the date and time include all the digits of pi.

## Alternative Pi Days and Pi Approximation Days

Pi Day and/or Pi Approximation Day can be celebrated on other calendar dates such as:

- July 22: When 22 is divided by 7, it equals 3.14.
- March 4: When 14% of the 3rd month has elapsed.
- April 5: When 3.14 months of the year have elapsed.
- April 26: The Earth has traveled two radians of its orbit on this day (April 25 in leap years). This is celebrated exactly on the 41st second of the 23rd minute of the 4th hour on April 26 or the 116th day. (In leap years, it is celebrated exactly on the 3rd second of the 2nd minute of the 12th hour on April 25 or the 116th day.)
- November 10: The 314th day of the year (November 9 in leap years).
- December 21, 1:13 p.m.: The 355th day of the year (December 20 in leap years), celebrated at 1:13 for the Chinese approximation 355/113.

## Pi Day Observances

Weekday | Date | Year | Name | Holiday type | Where it is observed |
---|---|---|---|---|---|

Wed | Mar 14 | 1990 | Pi Day | Worldwide observance | |

Sun | Jul 22 | 1990 | Pi Approximation Day | Worldwide observance | |

Thu | Mar 14 | 1991 | Pi Day | Worldwide observance | |

Mon | Jul 22 | 1991 | Pi Approximation Day | Worldwide observance | |

Sat | Mar 14 | 1992 | Pi Day | Worldwide observance | |

Wed | Jul 22 | 1992 | Pi Approximation Day | Worldwide observance | |

Sun | Mar 14 | 1993 | Pi Day | Worldwide observance | |

Thu | Jul 22 | 1993 | Pi Approximation Day | Worldwide observance | |

Mon | Mar 14 | 1994 | Pi Day | Worldwide observance | |

Fri | Jul 22 | 1994 | Pi Approximation Day | Worldwide observance | |

Tue | Mar 14 | 1995 | Pi Day | Worldwide observance | |

Sat | Jul 22 | 1995 | Pi Approximation Day | Worldwide observance | |

Thu | Mar 14 | 1996 | Pi Day | Worldwide observance | |

Mon | Jul 22 | 1996 | Pi Approximation Day | Worldwide observance | |

Fri | Mar 14 | 1997 | Pi Day | Worldwide observance | |

Tue | Jul 22 | 1997 | Pi Approximation Day | Worldwide observance | |

Sat | Mar 14 | 1998 | Pi Day | Worldwide observance | |

Wed | Jul 22 | 1998 | Pi Approximation Day | Worldwide observance | |

Sun | Mar 14 | 1999 | Pi Day | Worldwide observance | |

Thu | Jul 22 | 1999 | Pi Approximation Day | Worldwide observance | |

Tue | Mar 14 | 2000 | Pi Day | Worldwide observance | |

Sat | Jul 22 | 2000 | Pi Approximation Day | Worldwide observance | |

Wed | Mar 14 | 2001 | Pi Day | Worldwide observance | |

Sun | Jul 22 | 2001 | Pi Approximation Day | Worldwide observance | |

Thu | Mar 14 | 2002 | Pi Day | Worldwide observance | |

Mon | Jul 22 | 2002 | Pi Approximation Day | Worldwide observance | |

Fri | Mar 14 | 2003 | Pi Day | Worldwide observance | |

Tue | Jul 22 | 2003 | Pi Approximation Day | Worldwide observance | |

Sun | Mar 14 | 2004 | Pi Day | Worldwide observance | |

Thu | Jul 22 | 2004 | Pi Approximation Day | Worldwide observance | |

Mon | Mar 14 | 2005 | Pi Day | Worldwide observance | |

Fri | Jul 22 | 2005 | Pi Approximation Day | Worldwide observance | |

Tue | Mar 14 | 2006 | Pi Day | Worldwide observance | |

Sat | Jul 22 | 2006 | Pi Approximation Day | Worldwide observance | |

Wed | Mar 14 | 2007 | Pi Day | Worldwide observance | |

Sun | Jul 22 | 2007 | Pi Approximation Day | Worldwide observance | |

Fri | Mar 14 | 2008 | Pi Day | Worldwide observance | |

Tue | Jul 22 | 2008 | Pi Approximation Day | Worldwide observance | |

Sat | Mar 14 | 2009 | Pi Day | Worldwide observance | |

Wed | Jul 22 | 2009 | Pi Approximation Day | Worldwide observance | |

Sun | Mar 14 | 2010 | Pi Day | Worldwide observance | |

Thu | Jul 22 | 2010 | Pi Approximation Day | Worldwide observance | |

Mon | Mar 14 | 2011 | Pi Day | Worldwide observance | |

Fri | Jul 22 | 2011 | Pi Approximation Day | Worldwide observance | |

Wed | Mar 14 | 2012 | Pi Day | Worldwide observance | |

Sun | Jul 22 | 2012 | Pi Approximation Day | Worldwide observance | |

Thu | Mar 14 | 2013 | Pi Day | Worldwide observance | |

Mon | Jul 22 | 2013 | Pi Approximation Day | Worldwide observance | |

Fri | Mar 14 | 2014 | Pi Day | Worldwide observance | |

Tue | Jul 22 | 2014 | Pi Approximation Day | Worldwide observance | |

Sat | Mar 14 | 2015 | Pi Day | Worldwide observance | |

Wed | Jul 22 | 2015 | Pi Approximation Day | Worldwide observance | |

Mon | Mar 14 | 2016 | Pi Day | Worldwide observance | |

Fri | Jul 22 | 2016 | Pi Approximation Day | Worldwide observance | |

Tue | Mar 14 | 2017 | Pi Day | Worldwide observance | |

Sat | Jul 22 | 2017 | Pi Approximation Day | Worldwide observance | |

Wed | Mar 14 | 2018 | Pi Day | Worldwide observance | |

Sun | Jul 22 | 2018 | Pi Approximation Day | Worldwide observance | |

Thu | Mar 14 | 2019 | Pi Day | Worldwide observance | |

Mon | Jul 22 | 2019 | Pi Approximation Day | Worldwide observance | |

Sat | Mar 14 | 2020 | Pi Day | Worldwide observance | |

Wed | Jul 22 | 2020 | Pi Approximation Day | Worldwide observance |

## Quick Facts

Pi Day is observed every year on March 14 and July 22 in honor of the mathematical constant pi (π).### Pi Day 2015

Saturday, March 14, 2015Wednesday, July 22, 2015

### Pi Day 2016

Monday, March 14, 2016Friday, July 22, 2016

### Name in other languages

Name | Language |
---|---|

Pi Day | English |

Día de Pi | Spanish |

יום פאי | Hebrew |

يوم العدد ط | Arabic |

파이의 날 | Korean |

Pi-Tag | German |