Is Pi Wrong?

March 14, 2016 | Elizabeth Knowles

Pie with the number pi on top for Pi Day
Photo credit: Eric Sonstroem/Flickr (CC BY 2.0)

Mathematician Vi Hart thinks so.

Pi, 3.14159…, the number you learn in school as “the all-important circle constant” is wrong according to Mathematician Vi Hart.

When she says “wrong,” she doesn’t mean that pi as a number is wrong — you have learned some of the correct decimals for it and it works properly in the equations you memorized — it just isn’t the all-important constant it is made out to be.

SEE ALSO: Pi Found in Mathematical Calculation of the Hydrogen Atom

If it were up to Hart, students everywhere would be learning about tau (twice pi) instead. To demonstrate her reasoning, she gives the example of someone asking for pi/8 radians of a pie. You’d think that that might be an eighth of a pie, but really it’s a sixteenth. The whole pie, when you think of it in radians, isn’t pi — it’s 2pi, or tau.

As she admits, it’s not a complex conversion, but why are we making our lives more complicated than necessary? Hart emphasizes that it would make graphing trigonometric functions easier as well. If a whole circle represents tau, then halfway around the circle is simply tau/2.


It’s fun to eat pie on pi day, so Hart is not suggesting that you give up the celebration altogether. However, if you want to celebrate Tau Day on June 28, she has a great song about tau that you can listen to — and who doesn’t want another nerdy holiday to celebrate?


In her song Hart says, “We get further from truth when we obscure what we say. Math makes sense when it’s beautiful and pure!”

Hart isn’t the only one who believes this. Tau followers are called Tauists and the movement is based on two famous writings: “Pi is wrong,” by Bob Palais and “Tau Manifesto,” by Michael Hartl.

Many mathematicians feel strongly about pi and don’t like being told that it is wrong. They will tell you, for example, that although tau might make calculating a fraction of a circle easier in radians, pi works better for the area since the formula is pi * r2, making the area of a unit circle pi.

There are many other arguments on both sides, but they delve into more complex math. If you are interested, the Pi Manifesto has a good number of them.

Let us know which constant you prefer while you eat some pie — just try not to let it influence your decision!

You might also like: Graham’s Number Is Too Big to Explain How Big It Is

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