Jun28 Fun Holiday – Tau Day

Tau Day, an anti-Pi Day holiday, is an unofficial observance held every year since 2010 on June 28, or 06/28 as written in the American date format.

The day began as a way to recognize tau, τ, a ratio constant describing the relationship between the circumference and the radius of a circle. In recent years, some mathematicians and physicists have argued for the replacement of pi (π) by tau.

Replacing Pi

The concept of replacing pi by tau as a better way to describe the relationship between a circle’s circumference and its radius was first brought up by mathematics professor, Bob Palais in the Mathematical Intelligencer in an article called π is wrong!. This was followed by the publishing of the Tau Manifesto by physicist Michael Hartl. Both of these articles called for the replacement of pi by tau. Tau, the ratio of a circle's circumference to its radius, is equal to 2 π or 6.283.

Not Widely Accepted

Tau is not yet widely accepted within the scientific community, though there is a large community of scientists and technologists who have called for the replacement of pi by tau.

Other Mathematical Dates

The Gregorian Calendar is full of dates that when written in a special manner represent a mathematical or scientific concept. Some of these include Yellow Pig Day, Mole Day, Fibonacci Day, Palindrome Day, and e-Day. Use our Date Pattern Calculator to find out other interesting calendar dates during the year.

How to Celebrate?

• Because the value of tau is twice the value of pi, proponents of tau day call for “twice as much of pie” and to eat circular shaped food. So, instead of one slice of pie, eat two or four.
• If you are a teacher, use this day to encourage students to get interested in mathematics and to consider mathematics as a career choice.

Did You Know…

… that Michael Hartl, called for renaming March 14 (3/14) or Pi Day to Half Tau Day?

Tau Day Observances

Fun Holiday: Tau Day Observances
Year	Weekday	Date	Name
2024	Fri	Jun 28	Tau Day
2025	Sat	Jun 28	Tau Day
2026	Sun	Jun 28	Tau Day
2027	Mon	Jun 28	Tau Day
2028	Wed	Jun 28	Tau Day
2029	Thu	Jun 28	Tau Day
2030	Fri	Jun 28	Tau Day
2031	Sat	Jun 28	Tau Day
2032	Mon	Jun 28	Tau Day
2033	Tue	Jun 28	Tau Day

See all Fun Holidays