What Is Pi?

What is π?
I Like Pi

Screenshot via I Like Pi

What Is Pi (π)?

What Is Pi

Pi (3.14) is a ratio. A ratio is a statement of how two numbers compare. Pi is the ratio of the circumference of a circle compared to its diameter. It is found by dividing the circumference of a circle, or distance around a circle, to its diameter, or distance across a circle through it’s center. Pi = C/d.

Pi is always the same number no matter the size of the circle. The symbol for Pi is π and is pronounced  “pie”.


Pi Unrolled

The circumference of a circle is a little more than 3 times longer than its diameter. Always has been, always will be.

 Why isn’t Pi rational?

Pi is an irrational number, which means that it is a real number with decimal that repeats forever. There is no exact value for the number since it repeats infinitely.

Test it!

If you would like to investigate π on your own, try this brief experiment from Scientific American.

  1. Using a compass, draw a circle.
  2. Take one piece of string and place it on top of the circle, exactly once around.
  3. Straighten out the string; its length is called the circumference of the circle.
  4. Measure the circumference with a ruler.
  5. Measure the diameter of the circle, which is the length from any point on the circle straight through its center to another point on the opposite side. (The diameter is twice the radius, the length from any point on the circle to its center.)
  6. If you divide the circumference of the circle by the diameter, you will get approximately 3.14–no matter what size circle you drew!
  7. Now, retest larger circles.
  8. A larger circle will have a larger circumference and a larger radius, but the ratio will always be the same. If you could measure and divide perfectly, you would get 3.141592653589793238…, or pi.





Visual representations of Pi via Wikipedia

8 thoughts on “What Is Pi?

  1. We celebrate Pi Day by eating pies all day–mixed berry fruit pie for breakfast, with another fruit pie, tart cherry, being dessert in the eve. Lunch will be Dingle Pies, dinner is chicken pot pie. We LOVE Pi Day as we’re a pie family. 😀 And this is an extra special Pi Day due to the year — 3.14.15!! Hoping to get a picture of our clock precisely at 9:26 too. Won’t that be spectacular?? Have a happy Pi Day!!

      • OHMYGOODNESS–just went on wordpress.com after we ate the last piece of pi for Pi Day, read your response, looked at my computer to see how close it was to 3.1415926 and IT WAS 3.1415926!!!!!!!!! Awesomeness just happened. 🙂

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