Learn more fun facts on the Casual Pi Day Video Page.
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- Fun
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- AppreciationAwareness
- Where:
- United States
- Date change rule:
- Every July 22
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Casual Pi Day, also known as Pi Approximation Day, arrives every July 22. This day celebrates the mathematical constant Pi using the fraction 22/7 as its approximate value. Dive into the world of numbers, bake a delicious pie, and share your love for mathematics!
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Expected Casual Pi Day Deals
While we wait for official 2027 promotions to drop, history shows that many bakeries and restaurants often feature pie specials. Look for deals from chains like Marie Callender’s, Baker’s Square, and The Cheesecake Factory offering discounts on their delicious pies. Local pizzerias, such as Domino’s and Pizza Hut, might also offer ‘pizza pie’ deals. Keep an eye on grocery stores like Whole Foods Market and Kroger for sales on frozen pies and baking ingredients. We will update this page with confirmed live deals as July 22 approaches.
Platform Guide for Casual Pi Day
TikTok
Tag @www.nationaltoday.com and use #CasualPiDay. Film yourself baking a pie or sharing a fun math fact related to Pi.
Tag @nationaltoday_ and use #CasualPiDay. Share visually appealing photos of your favorite pies or creative ways you’re celebrating the mathematical constant.
X/Twitter
Mention @NatlToday and use #CasualPiDay. Tweet out interesting facts about Pi, challenge followers with math riddles, or share your pie-eating adventures.
Casual Pi Day Hero
Archimedes of Syracuse
History of Casual Pi Day
For roughly 4,000 years, pi has been known in some form or another. The ancient Babylonians used it to calculate the diameters of circles — about 3.125. Archimedes of Syracuse — one of the finest ancient mathematicians — computed pi for the first time about 250 B.C. He discovered that pi was between 3 1/7 and 3 10/71.
Later, in the mid-400s, another talented mathematician — Zu Chongzhi — used laborious computations to compute pi once more. Chongzhi invented his technique of calculating pi because Archimedes’ works were stolen and not available in China at the time. Chongzhi and Archimedes were the first scientists to discover pi in its true sense.
Later, mathematicians sought to improve the accuracy of pi by employing circumscribed and inscribed polygons. This is how Archimedes computed pi for the first time, and it remained the dominant algorithm for pi computation for the next 1,000 years. In 1630, Austrian astronomer, Christoph Grienberger, obtained the most accurate calculation of pi using this approach — arriving at 38 exact digits.
According to legend, Pi Approximation Day and Pi Day are inextricably linked, and Pi Day is celebrated on March 14 every year across the world. Because the value of Pi is 3.14, Physicist Larry Shaw established Pi Day in 1988 at the “Exploratorium.” According to the “San Francisco Science Museum,” the date for Pi Day has been set for 14 March, which is the number of the Pi (3.14). In 2009, the “United States House of Representatives” also backed Pi Day. The Pi Approximation Day, on the other hand, is observed every year on July 22.
Casual Pi Day timeline
Archimedes — a Greek mathematician — is credited with being the first person to successfully calculate pi after developing an algorithm around 250 B.C., which is why pi is also referred to as Archimedes' constant.
Computers compute pi to 31,415,926,535,897 decimal places, as well as its two-quadrillionth digit when represented in binary (0).
Lu Chao of China earns the “Guinness World Record” for reciting 67,890 digits of pi.
Haruka Iwao determines the world's most precise figure of pi which includes 31.4 trillion digits — breaking the previous record of 22 trillion.
How Businesses Can Celebrate Casual Pi Day
Local businesses can honor Casual Pi Day with creative promotions that blend math and fun. Bakeries and cafes could offer ‘Pi-themed’ specials like mini pies, pie-flavored lattes, or a 3.14% discount on certain items. Restaurants might introduce a special ‘pizza pie’ deal or a dessert menu featuring various sweet pies. Educational centers and bookstores could host math challenges or display books related to mathematics and its history. Encourage customers to share their celebrations on social media, tagging your business and using #CasualPiDay to amplify engagement.
Casual Pi Day FAQs
When is Casual Pi Day?
Casual Pi Day 2026 falls on a Wednesday, July 22. It’s a mid-week opportunity to celebrate the mathematical constant Pi with a slice of your favorite pie.
How is Pi used in everyday life?
Pi is fundamental in calculating the circumference and area of circles, which applies to countless real-world objects from wheels and pipes to satellite orbits and even the design of lenses. It’s also crucial in fields like engineering, physics, and computer graphics.
What is the difference between Pi Day and Casual Pi Day?
Pi Day is celebrated on March 14 (3/14), directly reflecting the first three digits of Pi (3.14). Casual Pi Day, or Pi Approximation Day, is observed on July 22, referencing the fraction 22/7, which is a common approximation of Pi.
How many digits of Pi are known?
As of early 2026, the known number of digits of Pi extends into the quadrillions. In 2024, a team at the University of Applied Sciences of the Grisons calculated Pi to 105 trillion digits, setting a new world record.
Casual Pi Day Activities
Have lots of pie
Remember that a pie is actually a circle, so you're not only learning mathematics but also having fun while eating it! Go on, dig in!
Participate in a contest
It has also been noted that many schools and education classes run contests to see whose student recalls Pi to the greatest number of decimal places. The person who knows the most digits in the number wins a pie.
Do some fun challenge
Schoolchildren and mathematicians alike like the challenge of memorizing as many digits of the number as possible! Today, challenge a friend or family member to outperform your knowledge of pi.
5 Interesting Facts About Pi
There is no zero
Pi's first 31 digits include no zeros.
6.4 billion known digits
Pi contains 6.4 billion known digits and it would take a human around 133 years to recite them all without pausing.
First letter of Greek word
Pi(π) is the initial letter of the Greek words ‘periphery’ and ‘perimeter.’
Sixteenth letter
Pi is the 16th letter in both the English and Greek alphabets.
Describe periodic phenomena
Pi is also employed in various physics and engineering formulas to explain periodic phenomena such as pendulum motion, string vibrations, and alternating electric currents.
Why We Love Casual Pi Day
Essential for fundamental calculation
It is required for the simple calculation of the circumference of a circle, but NASA also uses pi in several applications, such as calculating spaceship trajectories! Pi is a necessary constant in some of the most significant arithmetic.
Connect mathematics with the real world
Because pi is associated with circles, it is also associated with cycles, which include ebb and flow, ocean tides, electromagnetic waves, and many other things. Furthermore, many natural world events, such as the form of rivers, the disc of the sun, the helix of D.N.A., and even the pupil of an eye, may be estimated using pi.
We get to eat pie
Apart from how we may use this day as a fun challenge to remember pi, we must first consume a lot of pie before the challenges begin! Who cares about the scale?
Social Media Tips for Casual Pi Day
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