Pi Day takes place every year on 14 March (written 3/14 in month-day date format) to celebrate the math constant pi. Symbolized by the Greek letter π, pi shows the ratio of any circle’s distance around its edge to its width across, starting with the digits 3.14159. Physicist Larry Shaw created the holiday in 1988 at the San Francisco Exploratorium. Today, teachers, students, and math lovers worldwide mark the day by reciting numbers, solving fun puzzles, and sharing sweet or savory pies.

What is Pi Day?

Pi Day honors the math constant pi, written as the Greek letter π. Pi is the ratio of a circle’s outer edge to its width across the middle. No matter how big or small a circle is, that ratio always equals about 3.14159. Because pi is an infinite decimal that never ends or repeats, people love exploring its endless sequence of numbers.

The date 14 March was chosen because the American date layout, 3/14, matches the first three digits of pi. The day brings together school classes, science centers, and local clubs. People use the event to make math friendly, host pie baking games, and enjoy round treats with friends.

Teachers often use the day to show that math is part of daily life. From bike wheels and clock faces to pizza crusts, circles are everywhere. Celebrating pi gives everyone a fun reason to look closer at shapes and numbers.

Origins and the San Francisco Exploratorium

Physicist Larry Shaw started the first Pi Day in 1988 at the San Francisco Exploratorium museum. He worked there as a media specialist and wanted to make science fun for staff and guests. He planned a circular march around one of the museum rotundas at 1:59 p.m. to match 3.14159.

During that first gathering, staff members walked in circles while carrying signs and eating fresh fruit pies. The tradition grew larger each year at the museum. Soon, schools and colleges across the country picked up the idea, turning a simple staff break into a global tradition.

Official support came on 12 March 2009, when the United States House of Representatives passed House Resolution 224. The resolution recognized 14 March as National Pi Day. It urged schools to host events that build interest in science and math skills.

The History of the Number Pi

People knew about the link between a circle’s edge and width over 1000 years ago. Ancient Babylonian and Egyptian builders used simple ratios for circular structures. Around 250 BC, Greek thinker Archimedes of Syracuse (287–212 BC) found a close value for pi using 96-sided shapes.

Teacher William Oughtred first used the Greek letter π to stand for the ratio in 1647. Swiss thinker Leonhard Euler made the symbol famous across Europe when he used it in his 1737 books. Today, modern computers have calculated pi past 100 trillion digits.

The date 14 March also marks famous birthdays and events in physics. Famous scientist Albert Einstein was born on 14 March 1879 in Germany. Physics thinker Stephen Hawking passed away on 14 March 2018. These shared dates make 14 March a double feast for science lovers.

How People Celebrate Pi Day

Pi Day events mix school tests with light fun. The top memory challenge is reciting pi digits from memory. Contest leaders can speak thousands of decimal places without a single mistake.

Schools and local groups host pie baking contests. Bakers make fruit or cream pies decorated with the Greek symbol π. Many groups also hold pie eating races or pie toss games to raise money for school math clubs.

Bakeries and pizza shops often sell personal pies or pizza slices for $3.14. Running clubs also set up 3.14-mile fun runs, giving runners a healthy workout before they enjoy a slice of sweet pie.

Why Pi Day Matters for School STEM

Math can feel hard or dry to young students. Pi Day changes that by turning geometry into a hands-on game. Teachers use pie charts, wheel checks, and baking tasks to teach math ideas in a clear, friendly way.

Growing excitement for science and math helps solve big real-world problems. In 2019, UNESCO named 14 March the International Day of Mathematics. The move shows how math tools help build new technology, plan cities, and study climate patterns.

When students see how math links to food, art, and history, they gain confidence. A fun day with pie can inspire a lifelong interest in engineering, coding, or space science.

How to mark Pi Day

You can celebrate Pi Day at home or in class with these engaging activities.