Pi Approximation Day 2025: 17 Fascinating Facts You Need to Know About Pi

Every year on 22 July, math lovers around the world take a moment to celebrate something special—Pi Approximation Day. This day is dedicated to the mathematical constant π (pi), one of the most interesting and mysterious numbers we know. While most people have heard of Pi Day on 14 March (written as 3/14, like the first digits of pi), Pi Approximation Day is celebrated because 22/7 is a commonly used fraction that closely represents the value of pi.

This day is a reminder of the time that existed before modern technology, when mathematicians and scholars tried to understand the world around them using basic tools and clever thinking. They used simple ratios like 22/7 to work with pi long before anyone had access to calculators or computers. Even today, 22/7 is used as an easy way to work with pi in everyday calculations.

Pi is not just about circles—it appears in all kinds of places, from science and nature to music and architecture. It’s a number that seems simple at first but becomes more fascinating the more you learn about it. To mark the occasion of Pi Approximation Day 2025, here are 17 interesting and lesser-known facts about pi that will help you see just how special this number really is.

Every year, math enthusiasts around the world celebrate Pi Approximation Day on 22 July. While the more widely known Pi Day is observed on March 14 (3/14), Pi Approximation Day is just as important—and in some ways, more accurate. It honours the fractional value of 22/7, which is a well-known approximation of the mathematical constant π (pi).

What Exactly Is Pi?

Pi (π) is a mathematical constant that represents the ratio of a circle’s circumference to its diameter. No matter how big or small the circle is, this ratio is always the same—about 3.14159, although the digits go on forever without repeating.

Why Is It Called Pi Approximation Day?

Pi Approximation Day is celebrated on 22/7 (22nd July) because 22 divided by 7 gives an approximate value of 3.142857, which is close to the actual value of pi. It’s a way of recognising how ancient mathematicians tried to estimate pi long before we had computers.

Facts About Pi

• The exact value of Pi can never be calculated, that is why the accurate area or circumference of a circle can’t be determined.

• The symbol of Pi has been used for over 250 years. 

• William Jones was a Welsh mathematician who introduced the Pi symbol in 1706. 

• March 14 is celebrated as Pi day as 3.14 are the first digits of Pi. 

• The popular brand Givenchy sells a perfume named ‘Pi’. 

• Rajveer Meena of Vallore holds the record for memorising and reciting 70,000 decimal places of Pi. Guinness World Record mentions: “The most decimal places of Pi memorised is 70,000, and was achieved by Rajveer Meena (India) at the VIT University, Vellore, India, on 21 March 2015. Rajveer wore a blindfold throughout the entire recall, which took nearly 10 hours.”

• Civilisations like Babylonians and Egyptians used geometry to estimate Pi. 

• Not only is pi irrational, but it’s also transcendental, which means it is not the root of any non-zero polynomial equation with rational coefficients. This was proven in 1882 and finally put an end to ancient efforts to “square the circle.”

• The sequence 123456 doesn’t appear in the first million digits of Pi. 

• Larry Shaw who was a Physicist started the celebration of Pi Day on 14th March. 

• A British Mathematician William Shanks worked manually to find the digits of Pi in 1873. 

• Alberto Davila Argon rattled 280 words of Pi in one minute. 

• During World War II, the US and UK used Pi to send secret messages. 

• Pi is called a transcendental number. 

• In 2021, researchers in Switzerland ran a supercomputer for 108 days and calculated Pi to more than 62.8 trillion decimal places. 

• NASA only uses up to 16 digits of Pi to make calculations about the solar system. 

• There is a dialect known as Pilish which is created entirely from Pi.

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