MATHEMATICS · AGES 7+

Pie to Pi

Measure across a circular pie, follow its edge, and watch three diameters fit with a little extra.

Tap the picture to pause or play, or use the controls below. Sound is optional and off by default.

Pie → π a secret hidden in every circle across around a tiny bit! around ÷ across = 3 and a tiny bit = 3.14159… π Every circle, big or small!
0 seconds

Look, pause, wonder

Across means the diameter, passing through the centre. Around means the circumference. For a circle, circumference ÷ diameter = π, approximately 3.14. The rolling circle preserves its distance around; the cartoon crust and moving robot are a visual model, not a real measurement. Pi’s decimal continues without ending or a repeating block; a circle with a finite diameter still has a finite circumference.

Pause after the three blue lengths land. Why is there still a small length left over? What would double if the pie’s diameter doubled?

Read with Leo, Pip, and Gidget: From Apple Pie to Pi.

Explore the mathematics further · Back to the interactive collection