Pi symbol π

Divide any circle’s circumference by its diameter and you get the same number: π ≈ 3.14159265. It never ends or repeats, so formulas keep the symbol and round only at the last step.

• Circumference: C = πd or C = 2πr
• Area of a circle: A = πr². A 12-inch pizza (r = 6 in) has an area of about 113 square inches.
• Volume of a cylinder: V = πr²h

Americans celebrate Pi Day on March 14, because the US date 3/14 matches the first digits of π. The fraction 22/7 ≈ 3.142 is a handy approximation, accurate to two decimal places.

• Π (capital pi) is the Greek capital letter, the uppercase form of π in Greek text.
• ∏ (n-ary product) is the math operator for multiplying many terms together, the product counterpart of ∑. It is taller and belongs in formulas; in LaTeX it is \prod.
• ϖ (pi symbol) is a variant form, sometimes called curly pi, used in a few specialized formulas (\varpi in LaTeX).

The lowercase π you copy here is the Greek small letter pi, the right character for the constant. In plain text without symbols, write “pi.” In URLs and file names, also prefer “pi,” since some systems handle non-ASCII characters poorly.

• Android (Gboard): π is on the second symbols page.
• iPhone: add the Greek keyboard, or create a text replacement such as “pii” → π.
• Word: in an equation (Alt+=), type \pi and press space.
• LaTeX: \pi.
• Excel and Google Sheets: =PI() returns 3.14159265358979, so =PI()*A1^2 gives a circle’s area from its radius.
• Programming: Math.PI in JavaScript, math.pi in Python. Don’t hard-code 3.14 when the language gives you the full constant.