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- Every June 28
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Tau Day champions the mathematical constant tau (τ) every June 28. This day celebrates the ratio of a circle’s circumference to its radius, offering a fresh perspective on geometry. Join the growing movement of mathematicians and enthusiasts who believe tau is more intuitive than pi. Explore the arguments, share your insights, and celebrate the elegance of circles.
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History of Tau Day
The first known use of tau was approximated by Archimedes in the third century. He was born in the Greek city-state of Syracuse on the island of Sicily. Archimedes was known as one of the greatest scientists of the classical age, who, among many other things, calculated pi to the most precise value known. Pi is defined as the ratio of a circle’s circumference to its diameter as is tau, but some believe that Archimedes’ work would have been all the better if he had relied more on tau than pi.
During the eighteenth century, Leonhard Euler used the Greek letter π to represent the ratio of pi itself and for many years it has remained as the quintessential constant circle. This helped people understand circles, triangles, and other principles of geometry. It was a useful device that served its purpose well, but a new voice would define it as inelegant a couple of centuries later.
The tau movement was founded by the former University of Utah math professor Robert Palais who believed that tau simplified the math. Palais noticed that something was off with pi when calculating the sine of π/2 and the image he saw didn’t add up to the calculations. From this, he knew that pi wasn’t the way. Palais published his findings in a 2001 article titled “π is Wrong” in the “Mathematical Intelligencer.” He noted that Euler went back and forth between tau and pi, but pi became the accepted constant. Palais then proposed tau was superior and he used the pi symbol with an extra leg to represent it, and it eventually became an uppercase T.
On June 28, 2010, “The Tau Manifesto” launched at the same time as the first Tau Day. “The Tau Manifesto” was a book written by Michael Hart that was dedicated to the lesser-known number. In it, pi is referred to as unnatural and confusing. Pi compares a circle’s circumference with its diameter, and many mathematicians are disinterested in this quantity whereas tau is the number that connects a circumference to that quantity. The day is used to celebrate all of mathematics, but tau specifically still has an uphill battle in receiving recognition. If want to join the fight for tau, why not do a mathematics degree? here are some mathematics scholarships to help you.
Tau Day timeline
Famed mathematician and scientist Archimedes was the first person to approximate tau in his mathematics.
Mathematician Leonhard Euler used the Greek letter π to represent the ratio itself.
Robert Palais publishes his findings about tau and pi in an article titled "π is Wrong" in the magazine the “Mathematical Intelligencer.”
“The Tau Manifesto” is launched at the same time as Tau Day, dedicated to the lesser-known circle constant.
Tau Day FAQs
When is Tau Day?
Tau Day 2026 falls on Sunday, June 28, offering a weekend opportunity for mathematical exploration. It’s a day dedicated to celebrating the constant τ (tau), which is equal to 2π.
What is the value of Tau?
The mathematical constant tau (τ) is approximately 6.283185, representing the ratio of a circle’s circumference to its radius. This value is exactly double that of pi (π), which is approximately 3.14159.
Who started Tau Day?
Tau Day was initiated by Michael Hartl, a theoretical physicist, who published ‘The Tau Manifesto’ on June 28, 2010. His essay passionately argued for the adoption of tau over pi as the primary circle constant.
Why do some mathematicians prefer Tau over Pi?
Many mathematicians advocate for tau because it simplifies formulas involving radians, particularly in trigonometry and calculus. Since a full circle is 2π radians, using τ (which equals 2π) means a full circle is simply τ radians, making angular measurements more intuitive.
How To Celebrate Tau Day
Double it up
Since tau is twice the value of pi, it gives people the perfect excuse to eat double the amount of pie. Have your friends over for a pie party in the name of tau and try out an assortment of flavors, or you can make it a whole circular affair with circular-themed foods. Pizza, rice bowls, and meatballs can all honor tau. It can also inspire some interesting conversations depending on where your friends land on the debate between pi and tau.
Game of numbers
Make math fun by playing number games that will get you thinking. Bring the family together with a rousing game of dice that requires your math skills to win the game, or play the board game Mathological Liars where players earn points by solving mathematical mysteries.
Read the manifesto
Enlighten yourself by spending the day reading “The Tau Manifesto” and coming to your own conclusion about the answer. There are valid points on both sides, and the only way to know whether you’re a true believer of pi or tau is by knowing the information.
5 Interesting Facts About Tau Day
Tau of old
In ancient times, tau was used as a symbol for life or resurrection.
Double dates
Tau comes to the number (6.28) is twice as much as pi (3.14) which is why Tau Day is 6/28.
Ad Infinitum
Both tau and pi have an infinite amount of numbers.
Enough is enough
39 digits are enough to calculate the circumference of a circle.
Out of the shadows
Tau is growing in popularity as more people and professionals are beginning to recognize its merits.
Why We Love Tau Day
An alternate way of thinking
It’s important that we don’t become complacent in our mathematical beliefs. We should always question our processes as new ideas come about and that’s what tau represents. It doesn’t do any harm to test our knowledge to uncover what the true answers are. If one proves more correct, it will only advance the field, not hinder it.
A simpler kind of life
Tau is lauded as a constant that is more streamlined than its counterpart. With tau, everything matches up where it should be fractionally and it fixes radian angles which are chunks of a circle that were represented by unseemly fractions when pi was used. It’s believed that math is meant to be neat and complete, and taking that into regard, tau becomes that much more of a viable option.
Change isn’t that big of a deal
Many people don’t rely on using pi every day of their lives. For most people, it’s something that was used in school and then kept in a forgotten back closet in our minds. There’s no real harm in changing our approach and teaching the next generation that there are alternate methods to find answers.
