State of the Tau 2026

Tau’s Sweet Sixteen

Happy Tau Day, everyone!

When I first proposed using the Greek letter τ (tau) for the circle constant in 2010, I never imagined it would still be going so strong 16 years later. But here we are on 2026-06-28, and the number τ = C/r = 6.28… remains as relevant as ever. I’d especially like to express my gratitude to you, since Tau Day would be nothing without all the terrific tauists who’ve made it all the way to tau’s Sweet Sixteen.

And of course it’s twice as sweet with twice as much pie! 😋

In honor of tau’s Sweet Sixteen, please enjoy this year’s State of the Tau. In it you’ll find 16 tau celebrations, an intriguing report from “π Is Wrong!” author Bob Palais on tau-pilling Claude, a novel theory on the fall of the Roman Empire (?!), and more!

Michael Hartl
Founder, Tau Day
Author, The Tau Manifesto