The number π (/ paɪ / ⓘ; spelled out as pi) is a mathematical constant, approximately equal to 3.14159, that is the ratio of a circle 's circumference to its diameter.

Mar 2, 2026 · Pi, in mathematics, is the ratio of the circumference of a circle to its diameter. Because pi is irrational (not equal to the ratio of any two whole numbers), its digits do not repeat, and …

Then the circumference (all the way around the circle) is 3.14159265... a number known as Pi. Pi (pronounced like "pie") is often written using the Greek symbol π. With a diameter of D the …

May 17, 1999 · Succinctly, pi—which is written as the Greek letter for p, or π—is the ratio of the circumference of any circle to the diameter of that circle.

1 day ago · (WTAJ) — “Pi Day,” which is March 14, 3.14, is a day meant to recognize the special, infinite number that can also be recognized by its symbol π. Pi is an irrational number, which means it ...

Pi (often represented by the lower-case Greek letter π), one of the most well-known mathematical constants, is the ratio of a circle’s circumference to its diameter.

1 day ago · Saturday, March 14, 2026, is Pi Day, a national celebration of the mathematical concept.

3 days ago · For Pi Day, Mathematics Professor Adrian Rice answered our questions about the history and uses for the number pi.

Pi is an irrational number, which means you can’t write it as a simple fraction. Its decimal form goes on forever and never settles into a repeating pattern. No matter how far you go, the digits keep coming. …

Discover what pi (π) is and why it matters in math. Learn how it's used to calculate circumference, area, radians, and more. Simple explanations with examples.