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SatJun 28

Tau Day – June 28, 2025

Tau Day is celebrated on June 28. Once we know the story of this mathematical constant, we never look at a circle the same way again. Many people are aware that pi is the ratio of the circumference of any circle to the diameter of the circle, but there is a growing movement in favor of a new ratio taking its place tau. Tau is considered more accurate than pi, despite pi’s popularity. What’s even more interesting is a rumored conspiracy that the powers that be are holding steadfast to the concept of pi. Read on to learn more. 

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

3rd Century
Ancient Origins

Famed mathematician and scientist Archimedes was the first person to approximate tau in his mathematics.

It’s All Greek

Mathematician Leonhard Euler used the Greek letter π to represent the ratio itself.

No More Pi

Robert Palais publishes his findings about tau and pi in an article titled "π is Wrong" in the magazine the “Mathematical Intelligencer.”

June 28, 2010
Tau is Now

“The Tau Manifesto” is launched at the same time as Tau Day, dedicated to the lesser-known circle constant.

Tau Day FAQs

What is tau equal to?

What is Tau? The constant is numerically equal to 2*pi (2 times pi) and with value approximately 6.28. The ratio equates to 2*C/D.


What is tau vs pi?

At its heart, pi refers to a semicircle, whereas tau refers to the circle in its entirety.


What does tau mean in Chinese?

In Chinese, tau means the “way”, “path”, or “route” and can be philosophically metaphorical.

How To Celebrate Tau Day

  1. 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.

  2. 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.

  3. 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

  1. Tau of old

    In ancient times, tau was used as a symbol for life or resurrection.

  2. 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.

  3. Ad Infinitum

    Both tau and pi have an infinite amount of numbers.

  4. Enough is enough

    39 digits are enough to calculate the circumference of a circle.

  5. 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

  1. 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.

  2. 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.

  3. 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.

Tau Day dates

2025June 28Saturday
2026June 28Sunday
2027June 28Monday
2028June 28Wednesday
2029June 28Thursday

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