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Tau Day

Celebrate Tau Day and honor the mathematical constant - celebrate its beauty with puzzles, games, and activities!

Sunday

June 2026

Last updated February 7, 2026 · by the Holiday Calendar Team

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YEARLY DATEJune 28

OBSERVED INUnited States

CATEGORYSchool

SUBCATEGORYSTEM

INTRO

Introduction

PHOTO

Mark your calendars for June 28th and get ready to celebrate Tau Day! This day is dedicated to the mathematical constant tau, which is equal to 2π. It was first proposed in 2001 as an alternative to Pi Day (March 14th), which celebrates the ratio of a circle's circumference to its diameter. Since then, it has been adopted by mathematicians around the world who have embraced tau’s simplicity and elegance. So join us in celebrating this wonderful day with fun activities and mathematical puzzles that are sure to challenge your brain!

TIMELINE

Tau Day Timeline

Pi Emerges as a Constant

Pi, the ratio of a circle's circumference to its diameter, becomes a common mathematical constant in calculations and theoretical works.

Pi Day Celebration Begins

The first large-scale celebration of Pi Day is organized by physicist Larry Shaw at the San Francisco Exploratorium.

Tau is Proposed

Bob Palais publishes "π Is Wrong!" introducing tau (τ) as 2π, arguing that it is a more intuitive and useful constant when performing calculations involving circles and angles.

Tau Manifesto

Michael Hartl publishes "The Tau Manifesto," advocating for the use of tau instead of pi. Later the same year, he organizes the inaugural Tau Day on June 28.

Global Tau Day Celebrations

Each year on June 28, mathematicians and enthusiasts around the world celebrate Tau Day with activities, puzzles, and discussions on the merits of using tau over pi in calculations involving circles.

GET INVOLVED

How to Celebrate Tau Day

Organize a Pi and Tau party

Invite your friends over for a Pi and Tau party. Have games and activities that combine both numbers in some way. Make sure to have plenty of delicious pies and tau-shaped cookies.

CREATE

Create Tau-themed art

Grab some paints or markers and get creative! Paint or draw pictures of the tau symbol, or make an abstract piece inspired by its shape. You could even create a 3D model of it out of clay.

WATCH

Watch a movie about maths

Gather the family around the TV and watch a movie about maths. This could be anything from The Imitation Game to Good Will Hunting. Enjoy learning more about the wonders of mathematics.

READ

Read up on its history

Learn more about the history of the tau symbol; its origins, who first used it, why it was chosen, etc. You can find lots of information online or in books.

COMPETE

Compete in a tau quiz

Challenge your friends and family to a tau quiz! Put together a set of questions about its history, maths, or even pop culture references to the symbol and see who comes out on top.

WHY THIS DAY MATTERS

Why Tau Day is Important

Tau Day encourages curiosity

By observing Tau Day, people are reminded of the fascinating world of mathematics and encouraged to explore its mysteries further. It's also a great chance for anyone interested in math to learn something new by researching or discussing mathematical concepts with fellow enthusiasts!

Tau Day celebrates mathematical advances

Tau Day is a special day that is celebrated every year on June 28th to recognize and celebrate the importance of the number τ (tau). τ is a mathematical constant which is equal to 2π (it is sometimes abbreviated as t). This number plays an important role in many mathematical fields including calculus, trigonometry, and geometry.

Tau Day promotes STEM education

By introducing young students to τ through Tau Day, people are encouraging a greater appreciation for STEM topics like mathematics. This encourages more people to pursue careers in these areas and helpsscientists and mathematicians elevate their field even further.

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