Read the State of the Tau 2022 update  |

# No, really, pi is wrong… The Tau Manifesto

### by Michael Hartl

Tau Day is a celebration of the circle constant $\tau = C/r =$ $6.283185\ldots$ Founded in 2010 with the publication of The Tau Manifesto by Michael Hartl, Tau Day takes place annually on June 28 (6/28 in the American calendar system).

The Tau Manifesto’s introduction of $\tau$ (tau) as the “true circle constant” has had a significant impact on geek culture, including changing the time of day MIT announces its admissions decisions, being featured in the official Google calculator, and being supported by a large number of computer programming languages (including Microsoft .NET, Julia, Rust, and Python).

Including the English-language original, The Tau Manifesto is currently available in eight different languages. Its associated holiday, Tau Day, has been featured in The Wall Street Journal and is celebrated annually on 6/28 by thousands of math enthusiasts around the world.

To get all the latest updates on tau, read the State of the Tau update, and join the official Tau Email List.

## Tau Videos

Michael is ashamed to admit that he knows $$\pi$$ to 50 decimal places—approximately 48 more than Matt Groening. To atone for this, he has memorized 52 decimal places of $$\tau$$.