Pi (letter)

Greek alphabet

Αα Alpha	Νν Nu
Ββ Beta	Ξξ Xi
Γγ Gamma	Οο Omicron
Δδ Delta	Ππ Pi
Εε Epsilon	Ρρ Rho
Ζζ Zeta	Σσς Sigma
Ηη Eta	Ττ Tau
Θθ Theta	Υυ Upsilon
Ιι Iota	Φφ Phi
Κκ Kappa	Χχ Chi
Λλ Lambda	Ψψ Psi
Μμ Mu	Ωω Omega
Obsolete letters
Digamma	Qoppa
San	Sampi
Other characters
Stigma	Sho
Heta

Greek diacritics

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

Pi (uppercase Π, lower case π) is the sixteenth letter of the Greek alphabet. In the system of Greek numerals it has a value of 80. Letters that arose from pi include Cyrillic Pe (П, п).

In Modern Greek, the name of the letter is pronounced /pi/; in modern English, it is pronounced /paɪ/, in particular when referring to the mathematical constant (see below). In Greek the letter is pronounced /p/.

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.
In legal shorthand, it represents a plaintiff.

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 the 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
The natural projection on the tangent bundle on a manifold.

Variant pi or "pomega" ( $\varpi\,\!$ or ϖ) is a glyph variant of lower case pi sometimes used in technical contexts as though it were a lower-case omega with a macron, though historically it is simply a cursive form of pi, with its legs bent inward to meet. It is used as a symbol for:

The angular frequency of a wave in fluid dynamics (angular frequency is usually represented by $\omega$ but this may be confused with vorticity in a fluid dynamics context).
The longitude of pericenter in celestial mechanics.^[1]
Comoving distance in cosmology.^[2]

In HTML, the capital letter Π can be produced using the codes Π or Π, and the lower-case by using π or π within the source code.

Pi (letter)

See also

References