'I'm always looking for the Hows and the Whys and the Whats,' said Muskrat, 'That is why I speak as I do. You've heard of Muskrat's Much-in-Little, of course?'
'No,' said the child. 'What is it?'
- The Mouse and his Child. Russell Hoban.

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Wednesday, 30 June 2010

Tau equals Two Pi

Open your mouth wide like a circle, now say "Tau", and no more Pi for you!

I'm not a good mathematician. But I did know how to work out the length of the circumference and the area of a circle, if given the diameter. You simply used an incredibly complex number represented by the Greek letter π which is the ratio of the circumference to the diameter of any circle.

I was very interested to read an article today that suggests, nay proves, that π would be better thrown out and we should really work with a constant that is based, not on the diameter, but the radius. The Tau Manifesto by Michael Hartl, proposes the use of a new constant that is twice π, called Tau ($\tau$) instead of Pi (π).

ie. τ = 2π

A seemingly simple change. Yet, having introduced circle functions to 8 - 12 year-olds, I can tell you, Tau would be so much easier for young people (and everyone!) to understand and use than Pi.

It seems astonishing that something that we have used for so many centuries might be improvable.

You might like to read the Manifesto and make up your own mind.


  1. My dad always said, "Pi are not square; pi are wedge-shaped."

  2. Given the contents of the Manifesto rhymeswithplague's Dad was right on the ball.

    However to quote from the Manifesto: "Who cares whether we use pi or tau? It doesn’t really matter.
    Of course it matters. The circle constant is important. People care enough about it to write entire books on the subject, to celebrate it on a particular day each year, and to memorize tens of thousands of its digits. I care enough to write a whole manifesto, and you care enough to read it." Well that may be so but I, for one, will sick with pi. I've managed this far and I don't think I'll be changing. Come to think of it when did I last have to calculate the area of a circle? Hmmm.

  3. AGreenhill13.10.11

    Yes, the tau makes more sense. No, things won't change. It's far too infused, not just in science/engineering, but in culture.

    After reading the tau manifesto I was inspired to go back through my engineering textbooks. It was amazing how everywhere I looked I saw 2*PI. In the few places where PI was alone, it actually was enlightening to have the extra constant introduced into the equation because of tau.

    Later I went back through some of the fundamental physics identities/formulas that contain PI. Replacing it with tau would often introduced constants - but the constants actually made a lot of sense. If you're interested at all in this kind of stuff I encourage you to do this exercise yourself.

  4. Welcome to TLVD AG! And thank you for your comment. It's good to get a perspective from an engineer. And thanks for your recommendations. As I said, I am not a mathematician, but it seemed a sensible change to tau. Perhaps others will investigate it. Change does happen, albeit sometimes slowly.