Why the world needs pi

Share this page

Today, written as 3/14 the American way, is $\pi $ day! This special day happens every year, but today is extra special! It’s 3/14/15, giving us the first five digits of that lovely number, rather than just three! But why should we care about all these digits?

If you had a sloppy maths teacher at school you might have grown up with the idea that the number $\pi $ is equal to $22/7.$ Now that is completely wrong. Writing those numbers out in decimal gives $22/7 = 3.142...$ while $\pi = 3.141...$. There’s a difference in the third decimal place after the decimal point!


How accurately do we need to know the value of π?

Surely this small inaccuracy doesn't matter? Well, as the following extract from a longer article by Chris Budd shows, it really does.

The point is that $\pi $ is not any number. It lies at the heart of any technology that involves rotation or waves, and that is much of mechanical and electrical engineering. If rotating parts in, say, a typical jet engine are not manufactured to high tolerance, then the parts simply won’t rotate. This typically involves measurements correct to one part in 10,000 and, as these measurements involve $\pi $, we require a value of $\pi $ to at least this order of accuracy to prevent errors. In medical imaging using CAT or MRI scanners, the scanning devices move on a ring which has to be manufactured to a tolerance of one part in 1,000,000, requiring an even more precise value of $\pi $.

However, even this level of accuracy pales into insignificance when we look at modern electrical devices. In high frequency electronics, with frequencies in the order of 1GHz (typical for mobile phones or GPS applications), electrical engineers require a precision in the value used for $\pi $ in the order of one part in 1,000,000,000,000,000.

So, the modern world needs $\pi $ and it needs it accurately!

Read more about...


The term pi is a well known thing in all math classes. The number isn’t as simple as it sounds. It’s such a long number most teachers suggest you simplify it to 3.14. From reading this article I learned that pi also is used for useful things such as the common gps. It also helps save lives in the medical field with mri and cat scanners. Before reading this article I thought pi was simply just 3.14 with no real purpose, but after reading this I know that the term is way more than just an ordinary number.


Growing up in Nigeria, before moving to the UK, It was a taboo to forget that pi is 22/7. I am year 9 student. The fact that I have just found out that is so wrong and very much less precise has left really wandering what else I've really LEARNT wrong. The accuracy needed for pi in things like GPS and mobile phones which is a part of most people life, lays emphasis on its importance and should really be kept accurate and precise.

  • Want facts and want them fast? Our Maths in a minute series explores key mathematical concepts in just a few words.