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Pi Day

Quick Facts

Pi Day is annually observed on both March 14 and July 22 in honor of the mathematical constant pi (π).

Local names

NameLanguage
Pi DayEnglish
Día de PiSpanish
יום פאיHebrew
يوم العدد طArabic
파이의 날Korean
Pi-TagGerman

Pi Day 2014

Friday, March 14, 2014
Tuesday, July 22, 2014

Pi Day 2015

Saturday, March 14, 2015
Wednesday, July 22, 2015
List of dates for other years

Pi Day is the unofficial holiday that celebrates the mathematical constant pi (π) on March 14 in the month/day date format because the digits in this date correspond with the first three digits of π (3.14). It has become an international observance that is celebrated live and online and also celebrates Albert Einstein’s birthday.

Pi Approximation Day is held on July 22 in the day/month date format because it is the approximate value of π (22/7 = 3.14).

See other special calendar dates!

Pi Day celebrates the mathematical constant π (3.14) on March 14.

©iStockphoto.com/TheCrimsonMonkey

What is Pi (π)?

Pi (π) is the mathematical constant that has been known for almost 4000 years. Its value 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 because it is the first letter of the Greek work περίμετρος (perimeter), which probably refers to its use in the formula perimeter divided by diameter equals the constant for all circles. The concept of π has become the most common ground between mathematicians and non-mathematicians.

What do people do?

There are many activities that celebrate Pi Day such as games, creating some type of pi ambiance, eating “pi” foods, converting things into pi, making strange mathematical endeavors like having a contest to see who knows the most digits of pi. Many people celebrate Pi Day by eating pie and discussing the relevance of π. Many teachers will use this date to engage students in activities related to pi by singing songs and carols about pi and developing pi projects.

Mathematicians, teachers, museum directors, math students of all ages and other enthusiasts celebrate the number with pi recitations, pie-baking, pie-eating contests and math-related activities.

The First Pi Day

Pi Day celebrations was founded by Larry Shaw and it was first held at the San Francisco Exploratorium in 1988. The celebrations began with the public and museum staff marching around a circular space and then eating fruit pies. The museum has since then added pizza to its menu and has grown to include activities such as creating Pi puns, Pi-related antics, and many other activities that involve Pi.

Alternative Pi Days and Pi Approximation Days

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

Pi Day Observances

WeekdayDateYearNameHoliday typeWhere it is observed
WedMar 141990Pi DayWorldwide observance 
SunJul 221990Pi Approximation DayWorldwide observance 
ThuMar 141991Pi DayWorldwide observance 
MonJul 221991Pi Approximation DayWorldwide observance 
SatMar 141992Pi DayWorldwide observance 
WedJul 221992Pi Approximation DayWorldwide observance 
SunMar 141993Pi DayWorldwide observance 
ThuJul 221993Pi Approximation DayWorldwide observance 
MonMar 141994Pi DayWorldwide observance 
FriJul 221994Pi Approximation DayWorldwide observance 
TueMar 141995Pi DayWorldwide observance 
SatJul 221995Pi Approximation DayWorldwide observance 
ThuMar 141996Pi DayWorldwide observance 
MonJul 221996Pi Approximation DayWorldwide observance 
FriMar 141997Pi DayWorldwide observance 
TueJul 221997Pi Approximation DayWorldwide observance 
SatMar 141998Pi DayWorldwide observance 
WedJul 221998Pi Approximation DayWorldwide observance 
SunMar 141999Pi DayWorldwide observance 
ThuJul 221999Pi Approximation DayWorldwide observance 
TueMar 142000Pi DayWorldwide observance 
SatJul 222000Pi Approximation DayWorldwide observance 
WedMar 142001Pi DayWorldwide observance 
SunJul 222001Pi Approximation DayWorldwide observance 
ThuMar 142002Pi DayWorldwide observance 
MonJul 222002Pi Approximation DayWorldwide observance 
FriMar 142003Pi DayWorldwide observance 
TueJul 222003Pi Approximation DayWorldwide observance 
SunMar 142004Pi DayWorldwide observance 
ThuJul 222004Pi Approximation DayWorldwide observance 
MonMar 142005Pi DayWorldwide observance 
FriJul 222005Pi Approximation DayWorldwide observance 
TueMar 142006Pi DayWorldwide observance 
SatJul 222006Pi Approximation DayWorldwide observance 
WedMar 142007Pi DayWorldwide observance 
SunJul 222007Pi Approximation DayWorldwide observance 
FriMar 142008Pi DayWorldwide observance 
TueJul 222008Pi Approximation DayWorldwide observance 
SatMar 142009Pi DayWorldwide observance 
WedJul 222009Pi Approximation DayWorldwide observance 
SunMar 142010Pi DayWorldwide observance 
ThuJul 222010Pi Approximation DayWorldwide observance 
MonMar 142011Pi DayWorldwide observance 
FriJul 222011Pi Approximation DayWorldwide observance 
WedMar 142012Pi DayWorldwide observance 
SunJul 222012Pi Approximation DayWorldwide observance 
ThuMar 142013Pi DayWorldwide observance 
MonJul 222013Pi Approximation DayWorldwide observance 
FriMar 142014Pi DayWorldwide observance 
TueJul 222014Pi Approximation DayWorldwide observance 
SatMar 142015Pi DayWorldwide observance 
WedJul 222015Pi Approximation DayWorldwide observance 
MonMar 142016Pi DayWorldwide observance 
FriJul 222016Pi Approximation DayWorldwide observance 
TueMar 142017Pi DayWorldwide observance 
SatJul 222017Pi Approximation DayWorldwide observance 
WedMar 142018Pi DayWorldwide observance 
SunJul 222018Pi Approximation DayWorldwide observance 
ThuMar 142019Pi DayWorldwide observance 
MonJul 222019Pi Approximation DayWorldwide observance 
SatMar 142020Pi DayWorldwide observance 
WedJul 222020Pi Approximation DayWorldwide observance 
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