Pi Day Activity: Finding Pi

Read Sir Cumference and the Dragon of Pi with your child. It’s not only a great story, but also a clever way to help children understand pi (π). In the story, Sir Cumference drinks a potion that accidentally turns him into a dragon. His son, Radius, must find a cure. Along the way, he meets Geo and Sym Metry, brothers who make wheels, he helps his cousin, Lady Fingers bake pies and he solves the mystery of pi.

Have your child try what Radius did in the story. First have them pick a round snack. Take a piece of string and measure the diameter (d) of the chosen snack.

Have your child carefully triple the length of string. Essentially, they’re multiplying the diameter by three. Cut the string.

Ask your child to wrap the string around the outside of the round snack. It won’t reach all the way around — there’s a gap, just like when Radius tried to use three lengths of pie crust to make the outside circle of the wheel in the story. Three lengths isn’t quite enough. Ask your child to guess how much more string he needs.

The answer? It’s that extra .14159265359… that defines the number pi and lets the string reach all the way around a circle. Try again with other round snacks!