Pi Approximation Day 2025: What is the story behind Pi Day?

Jul 22, 2025, 13:49 IST

Pi Approximation Day 2025 is observed on 22 July every year. It’s also sometimes called Casual Pi Day. This day is all about recognizing and appreciating the mathematical constant pi (π), which is used in many areas of math and science. The date, 22/7, is chosen because the fraction 22 divided by 7 gives an approximate value of pi, which is about 3.14. While it’s not the exact value of pi, 22/7 is a close and simple way to understand it. Pi Approximation Day gives us a chance to explore the importance of pi, how it works, and where we use it in everyday life—from circles and geometry to physics and engineering. Let’s take a closer look at the meaning behind this day and why pi continues to be such a fascinating number.

Pi Approximation Day
Pi Approximation Day

Pi Approximation Day 2025: Pi is a special number in mathematics. It shows the relationship between a circle’s circumference (the distance around the circle) and its diameter (the distance across the circle through the centre). No matter how big or small the circle is, this ratio is always the same—pi, often written as the symbol π. The symbol π was first introduced in 1706 by a British mathematician named William Jones. Later on, it became more widely used and well-known thanks to a famous Swiss mathematician, Leonhard Euler, who helped popularise it in his work.

We observe Pi Approximation Day on 22 July every year. This date is special because when you divide 22 by 7, you get a number that is very close to the actual value of pi (which is about 3.14159). Since 22/7 is a convenient way to remember and use pi in calculations, this day is set aside to recognise its significance. That’s why it’s also sometimes called Casual Pi Day—a more relaxed way of celebrating pi without diving into its more complex digits.

What is the story behind Pi Approximation Day?

Pi Approximation Day is celebrated on July 22nd because it coincides with the fraction 22/7, which is often used as an approximation for the mathematical constant π (pi). The value of π is a fundamental constant that represents the ratio of a circle's circumference to its diameter. It is an irrational number, meaning it cannot be expressed as a simple fraction, and its decimal representation goes on infinitely without repeating.

The value of π is approximately 3.14159, but the fraction 22/7 is a common approximation that yields 3.142857... when calculated. While 22/7 is not as accurate as the true value of π, it is simple and easy to remember, making it a popular approximation used in various calculations, particularly in early mathematics education.

Pi Approximation Day is an informal and fun way to celebrate mathematics and the fascinating properties of π. It provides an opportunity for math enthusiasts, educators, and students to appreciate the significance of this fundamental constant and its applications in various fields such as geometry, trigonometry, calculus, and physics.

It's worth noting that Pi Day, which is celebrated on March 14th (3/14 in month/day date format), is a more widely recognized celebration of the mathematical constant π. Pi Day gained popularity thanks to its numerical resemblance to the first three digits of π (3.14). However, Pi Approximation Day on July 22nd offers an alternative opportunity to celebrate π and promote interest in mathematics.

Pi Approximation Day: Quotes

1. "We cannot hope that many children will learn mathematics unless we find a way to share our enjoyment and show them its beauty as well as its utility." - Mary Beth

2. "It’s exact and indefinite. It’s like pi- you can keep figuring it out and always be right and never be done." -  Unknown

3. "Pi is not merely the ubiquitous factor in high school geometry problems; it is stitched across the whole tapestry of mathematics, not just geometry’s little corner of it." -  Unknown

4. “Errors using inadequate data are much less than those using no data at all.” - Charles Babbage

5. “Mathematicians are like managers – they want improvement without change.” - Edsger Dijkstra

6. “Mathematicians stand on each other’s shoulders.” - Carl Friedrich Gauss

7. “What is imagination?…It is a God-like, a noble faculty. It renders earth tolerable, it teaches us to live, in the tone of the eternal.”- Ada Lovelace

8. "The Great Pyramid, that monument to spirituality that the Agashan Teachers hold in such high esteem, is built according to Pi’s principles." - William Eisen

9. "Exploring pi is like exploring the universe." - David Chudnovsky

10. "Pi is not merely the ubiquitous factor in high school geometry problems; it is stitched across the whole tapestry of mathematics, not just geometry’s little corner of it." - Robert Kanigel

According to timeanddate.com, the day depends upon the format of the Date. In some countries where people write their dates in the date/month format celebrate Pi Approximation Day or Casual Pi Day on 22 July or 22/7. And on the other hand, those who write their date in month/date format celebrate Pi Day on 14 March (3/14 or 3-14). It is because the first three digits of the date correspond to the first three digits of pi (3.14).

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

Nikhil Batra
Nikhil Batra

Content Writer

Nikhil comes from a commerce background, but his love for writing led him on a different path. With more than two years of experience as a content writer, he aspires to breathe life into words. He completed his B.Com. from DU and finds joy in traveling and exploring new and hidden places. Do drop your feedback for him at nikhil.batra@jagrannewmedia.com and let him know if you love his work

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FAQs

  • Who devised the symbol π?
    +
    π symbol was devised by British mathematician William Jones in 1706 to represent the ratio and later it was popularised by the Swiss mathematician Leonhard Euler.
  • Who devised the symbol π?
    +
    π symbol was devised by British mathematician William Jones in 1706 to represent the ratio and later it was popularised by the Swiss mathematician Leonhard Euler.
  • What is the value of pi to 39 decimal places?
    +
    The value of pi to 39 decimal places is 3.141592653589793238462643383279502884197.
  • What is the value of pi to 39 decimal places?
    +
    The value of pi to 39 decimal places is 3.141592653589793238462643383279502884197.
  • What is Pi Approximation Day observed?
    +
    Pi Approximation Day is observed on 22 July and is also known as Casual Pi Day. The day is dedicated to the mathematical constant pi (π).
  • What is Pi Approximation Day observed?
    +
    Pi Approximation Day is observed on 22 July and is also known as Casual Pi Day. The day is dedicated to the mathematical constant pi (π).

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