A playful tour of π
π is Fun.
You learned that π is "about 3.14" — the ratio between a circle's edge and the line across it. But how do we actually find it? Turns out, in lots of beautiful ways.
It all started in 250 BC with Archimedes
Hexagon — where Archimedes began
Each side of the inscribed hexagon equals the radius, so its half-perimeter is exactly 3. A surprisingly clean starting point — and the reason he chose it.
Drag the slider. Watch the polygons hug the circle. That gap closing? That's π getting more accurate.
Why a whole site about π?
Because π keeps showing up in places it has no business being. You'd expect it in circles. But it also appears in probability, in dropped needles, in random dots, in infinite sums of fractions that have nothing to do with circles at all.
Each page here picks one of those methods and lets you play with it. No equations are required to enjoy the pictures — but if you're curious, the math is right there too.
Ways to find π
From ancient geometry to modern probability.
Squeezing with polygons
~250 BC · ArchimedesTrap the circle between two polygons. As you add sides, the polygons close in on π from both sides.
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Throwing darts
~1940s · Monte CarloToss random points into a square and count how many land inside a circle. The ratio tells you π. (Yes, really.)
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An infinite sum of fractions
~1670 · Leibnizπ/4 = 1 − 1/3 + 1/5 − 1/7 + … Add the fractions forever and you get π. Almost magic.
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Dropping needles on lines
1777 · BuffonDrop needles on a lined floor. Count the ones that cross a line. Out pops π. Nobody saw this coming.
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A faster infinite series
~1500 · NilakanthaA clever Indian mathematician's series that beats Leibniz to good digits in a fraction of the steps.
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Going deeper
Big-picture pages that aren't tied to one calculation method.
Why π matters
Real-world places it shows upSpacecraft, signals, statistics, quantum mechanics — and how few digits we actually need.
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Computers and π
How the chase changed in the 1900sFrom slide rules and ENIAC to today's 100-trillion-digit records — the algorithms and machines behind the modern π race.
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Resources
Books, papers, sites, talksCurated further reading. Everything cited, everything reputable, all in one place.
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So — is π fun?
Look: if you don't think π is fun after clicking around here, either it's just not for you, or we've still got work to do.
But what makes anything fun, really? The chase. Finding new ways to do the same old thing.
Later in life, I got into birds. Birds had always been around — nothing about them had changed. But once you spot a cardinal against the snow a couple of times, you start to notice birds everywhere. You get more interested. You look harder. You see more.
π works the same way. π is everywhere once you start looking — in circles, sure, but also in waves, in probability, in how your phone hears you, in the very structure of physical reality. So keep an eye out.
π is fun.