Pi Approximation Day
22/7 — the fraction that has approximated pi for over 2,000 years.
About
Pi Approximation Day on July 22 celebrates the fraction 22/7, which provides a convenient approximation of π (pi ≈ 3.14159...). When written in day/month format as 22/7, the date represents this ancient approximation used by mathematicians and engineers for centuries. While March 14 (3/14) is the primary Pi Day celebration, July 22 offers mathematicians in countries using the day/month format an alternative date to celebrate their favourite constant.
History
The approximation 22/7 dates to Archimedes of Syracuse, who in the 3rd century BCE established that π lies between 223/71 and 22/7 — a remarkable achievement using only geometric reasoning. The 22/7 approximation (3.142857...) differs from the true value by less than 0.04%. Pi Approximation Day as a celebration emerged informally among mathematics communities in the 1990s-2000s.
Where It's Observed
Cultural Context
US United States
Americans primarily celebrate Pi Day on March 14, but Pi Approximation Day is observed in academic circles. Math teachers use it as a second chance to engage students with the history of π and the concept of approximation in mathematics.
KR South Korea
Korean students encounter 22/7 as pi's approximation in mathematics curriculum. Pi Approximation Day is increasingly known in Korean math education communities, and online discussions about pi's digits and mathematical history spike on the date.
JP Japan
Japan writes dates in year/month/day format, making neither 3/14 nor 22/7 'natural' pi dates. Nevertheless, Japanese mathematics communities celebrate both occasions, and the precision-loving culture embraces the irony of approximating an irrational number.
How to Participate
- 01Calculate 22/7 and compare it to pi — notice how close the approximation is
- 02Learn about Archimedes' method for estimating pi without a calculator
- 03Try computing pi using a simple Monte Carlo simulation
- 04Discuss with children why an 'exact' value of pi is mathematically impossible
Frequently asked questions
When is Pi Approximation Day?+
Pi Approximation Day is observed annually on July 22. The date is fixed each year — July 22 — and does not shift based on the lunar calendar or weekday.
What is Pi Approximation Day?+
Pi Approximation Day on July 22 celebrates the fraction 22/7, which provides a convenient approximation of π (pi ≈ 3.14159...). When written in day/month format as 22/7, the date represents this ancient approximation used by mathematicians and engineers for centuries. While March 14 (3/14) is the pr…
Is Pi Approximation Day a public holiday?+
Pi Approximation Day is an international observance or awareness day, not a public holiday in most countries. It does not typically result in days off work or school closures, though some countries and organisations hold official events.
How can I participate in Pi Approximation Day?+
Calculate 22/7 and compare it to pi — notice how close the approximation is Learn about Archimedes' method for estimating pi without a calculator Try computing pi using a simple Monte Carlo simulation These are some of the most accessible ways to engage with the day's purpose.
Which countries observe Pi Approximation Day?+
Global — especially popular in countries using day/month format.
Mark the date
Download a free printable calendar for 2026 and never miss Pi Approximation Day.