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Greek alphabet
Α α Alpha	Ν ν Nu
Β β Beta	Ξ ξ Xi
Γ γ Gamma	Ο ο Omicron
Δ δ Delta	Π π Pi
Ε ε Epsilon	Ρ ρ Rho
Ζ ζ Zeta	Σ σ ς Sigma
Η η Eta	Τ τ Tau
Θ θ Theta	Υ υ Upsilon
Ι ι Iota	Φ φ Phi
Κ κ Kappa	Χ χ Chi
Λ λ Lambda	Ψ ψ Psi
Μ μ Mu	Ω ω Omega
Obsolete letters
Ϝ ϝ Digamma	Ϻ ϻ San
Ϙ ϙ Qoppa	Ϡ ϡ Sampi
Ϛ ϛ Stigma	Ϸ ϸ Sho

This article is about the letter π. For the mathematical pi, see Pi. And for other uses, see Pi (disambiguation)

Pi (upper case Π, lower case π or ϖ) is the sixteenth letter of the Greek alphabet. In the system of Greek numerals it has a value of 80.

In Greek, the letter is pronounced /piː/ (as in pee); in modern English, it is pronounced /paɪː/ (as the word pie), in particular when referring to the mathematical constant (see below). In words, it is pronounced /p/. In Modern Greek, the sequence of letters μπ represents the /b/ sound, as in boy (the second letter of the Greek alphabet is now pronounced /v/ as in very).

There is another variant of lower case Pi, resembling a lower case Omega: <math>\varpi\,\!</math>.

The upper-case letter Π is used as a symbol for:

• The product operator in mathematics, indicated with capital pi notation ∏ (in analogy to the use of the capital Sigma Σ as summation symbol).
• In textual criticism, Codex Petropolitanus, a 9th century, uncial codex of the Gospels, now located in St. Petersburg, Russia.

The lower-case letter π is used as a symbol for:

• The mathematical irrational constant π ≈ 3.14159..., the ratio of a circle's circumference to its diameter in Euclidean geometry. The letter "π" is first letter of the Greek words "περιφέρεια" 'periphery' and "περίμετρος" 'perimeter', i.e. the circumference.
• The prime counting function in mathematics.
• Dimensionless parameters constructed using the Buckingham π theorem of dimensional analysis.
• The osmotic pressure in chemistry. π=MRT
• The elementary particle called the pi meson or pion.
• Profit in microeconomics.
• Inflation rate in macroeconomics.
• A type of chemical bond in which the P-orbitals overlap

In HTML, the capital letter Π can be produced using the codes &Pi; or &#928;, and the lower-case by using &pi; or &#960; within the source code.als:Π br:Pi (lizherenn) bg:Пи (буква) ca:Π da:Pi (bogstav) de:Pi (Buchstabe) arc:Π el:Πι es:Π eu:Pi (greko) fr:Pi (lettre grecque) gd:Pi gl:Pi (letra) ko:Π he:פאי (אות) hu:Pi nl:Pi (letter) ja:Π nn:Π nds:Pi pl:Pi (litera) pt:Π ru:Пи (буква) sk:Pí (písmeno) sv:Pi (bokstav) zh:Π