Roll Out the Simplest Mathematics Activity for Pi Day


Home / Roll Out the Simplest Mathematics Activity for Pi Day
Star Trek Enterprise Pizza Cutter : image by joebeone (Joe Hall)

You can use a pizza cutter (even one that looks like the Starship Entreprise) to calculate Pi. Image by Joe Hall

How to Roll Out Pi

The Star Trek Enterprise pizza cutter is a fine example of a wheel that’s easy to turn. A spool of thread, or even a coin, can also work.

Prepare a log page to record the results. The columns should include: a name for each wheel, its diameter, the length of the circumference, and the calculated ratio for pi. You can also include a column for the difference from pi, which is the measurement error.

Start by marking a long straight line on the paper for the wheel to follow.

Measure the diameter, ‘d’, of each wheel before dabbing on any ink.

For each wheel, add enough ink on one spot to leave a couple of marks on the paper. Roll the wheel forward to make those marks. Measure the distance from the start of one mark and the start of the next: that’s the circumference ‘C’. It’s best to ink, roll and measure each wheel separately.

All that’s left is cleaning off the ink and doing the math to calculate π=C/d.

An Alternative Way to Roll Out Pi

If an appropriate ink is difficult to find, or the paper isn’t long enough, this alternative method avoids rolling the wheels. Rather than ink, it uses paper, scissors and tape.

Measure the diameter of the wheel and set up the table for results just as in the first method, but don’t ink or roll the wheel.

Instead, cut a strip of paper. Wrap it around the wheel and tape it to keep the overlap secure. Remove the paper circle from the wheel and cut it somewhere opposite the tape. Measure the straight length of the paper strip; that’s the circumference ‘C’. Log the values and do the calculations for π=C/d.

Celebrating Pi Day

There are many fun and creative ways to calculate pi, from the Buffon Needle Drop experiment to various simple pi rolling tests. Although pi is very important in mathematics, the most memorable way to celebrate the 14th of March is to eat a slice of pi day pie. Others will take part in commemorative events or wear ‘Pi Day’ shirts from the official Pi Day website.


Smoller, Laura. The Amazing History of Pi. (2001). University of Arkansas at Little Rock. Accessed February 24, 2013.

Pi Day. Celebrate March 14. (2013). Accessed February 24, 2013.

Leave a Comment