When is Pi Day?
Pi Day falls on March 14 every year. In the month/day date format used in the United States, March 14 is written 3/14, matching pi’s first digits, 3.14. Enthusiasts often mark the exact moment at 1:59 p.m., which extends the match to 3.14159.
| Year | Date | Day of the week |
|---|---|---|
| 2027 | March 14, 2027 | Sunday |
| 2028 | March 14, 2028 | Tuesday |
| 2029 | March 14, 2029 | Wednesday |
| 2030 | March 14, 2030 | Thursday |
In countries that write the day first (14/3), the date does not spell out pi — but Pi Day is celebrated on March 14 around the world anyway.
The history of Pi Day
Pi Day began in 1988 at the Exploratorium, the science museum in San Francisco. Physicist Larry Shaw organised a small celebration in which staff walked around a circular space and shared fruit pies. The museum kept the tradition going, and over the following decades it spread to schools, universities and maths fans everywhere.
In 2009, the United States House of Representatives passed a resolution recognising March 14 as National Pi Day, encouraging schools to use the day to get students interested in mathematics.
The date has a few other connections that fans love to point out: Albert Einstein was born on March 14, 1879, and physicist Stephen Hawking died on March 14, 2018.
Pi Day and the International Day of Mathematics
In 2019, UNESCO proclaimed March 14 the International Day of Mathematics. It was first celebrated in 2020, and each year it promotes the role of mathematics in science, technology and everyday life. So March 14 is now both an informal celebration of one famous number and an official celebration of mathematics as a whole.
How to celebrate Pi Day
You don’t need to be a mathematician. A few ideas, from easy to ambitious:
At home
- Eat something round. Pie is traditional; pizza counts too. Measure it first: is the crust really about 3.14 times the width?
- Measure pi yourself. Wrap a string around a jar, a plate and a bike wheel, then divide each length by the width. Every answer should land near 3.14.
- Learn some digits. Try to memorize the first 20 — use the tips on our digits of pi page.
- Find your birthday in pi. Search for your date as digits in PI Explorer. About 63% of all six-digit sequences appear within the first million decimals.
In the classroom
- Circle measuring lab. Groups measure circular objects, record circumference ÷ diameter, and average the class’s results.
- Pi recitation contest. Give students a week to learn as many digits as they can.
- Estimate pi with randomness. Drop grains of rice on a square with a quarter circle drawn in it. Four times the share that lands inside the curve approximates pi — the idea behind Monte Carlo methods.
- Explore the history. Compare Archimedes’ polygon method with modern algorithms in how pi is calculated.
At 1:59 p.m.
Take a moment at 1:59 p.m. on March 14 — 3/14 1:59 — for a pi-themed toast, a slice of pie, or a scroll through a million digits of pi.
Fun facts about pi for Pi Day
- Pi’s decimals never end and never repeat — it was proved irrational in 1761.
- NASA’s JPL uses only 15 decimal places of pi (3.141592653589793) for interplanetary navigation.
- Six 9s in a row appear at decimal positions 762–767. It is called the Feynman point.
- The first 0 in pi’s decimals does not appear until position 32.
- Pi’s own opening digits, 314159, appear again at position 176,451.
- The symbol π was first used for this number in 1706 and made popular by Leonhard Euler.
- Computers have calculated pi to well over 100 trillion digits.
Want more? See notable places in the digits of pi and the mathematics of π.
Pi Day questions
Why is Pi Day on March 14?
Because March 14 is written 3/14 in month/day format, matching the first three digits of pi, 3.14.
Who started Pi Day?
Physicist Larry Shaw started Pi Day at the San Francisco Exploratorium in 1988.
Is Pi Day a public holiday?
No. It is an informal celebration recognised by a 2009 US House resolution, and since 2020 March 14 has also been UNESCO’s International Day of Mathematics. Schools and offices stay open.
What time is Pi Day celebrated?
Many fans celebrate at 1:59 p.m., because 3/14 1:59 matches the first six digits of pi: 3.14159.
Celebrate with the digits
Find your birthday in a million digits of π.