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Many letters of theLatin alphabet, both capital and small, are used inmathematics,science, andengineering to denote by convention specific or abstracted constants, variables of a certain type, units, multipliers, or physical entities. Certain letters, when combined with special formatting, take on special meaning.

Below is an alphabetical list of the letters of the alphabet with some of their uses. The field in which the convention applies is mathematics unless otherwise noted.

Some common conventions:

• Intensive quantities inphysics are usually denoted withminuscules
  whileextensive are denoted withcapital letters.
• Most symbols are written initalics.
• Vectors can be denoted inboldface.
• Sets ofnumbers are typically bold orblackboard bold.

• A represents:
  • the first point of atriangle^[1]
  • the digit "ten" inhexadecimal^[2] and other positional numeral systems with a radix of 11 or greater^[3]
  • the unitampere for electric current inphysics^[4]
  • thearea of a figure^[5]
  • themass number ornucleon number of an element inchemistry^[6]
  • theHelmholtz free energy of a closed thermodynamic system of constant pressure and temperature^[7]
  • avector potential, in electromagnetics it can refer to themagnetic vector potential^[8]
  • with a subscript, analternating group on that many objects
  • anAbelian group in abstract algebra
  • theGlaisher–Kinkelin constant^[9]
  • atomic weight, denoted byA_r^[10]
  • work inclassical mechanics^[10]
  • thepre-exponential factor^[10] in theArrhenius Equation^[11]
  • electron affinity^[10]
• ${\displaystyle \mathbb{A}}$ represents thealgebraic numbers^[12] or affine space inalgebraic geometry.
  • Ablood type
  • Aspectral type
• a represents:
  • the first side of a triangle (opposite point A)^[1]
  • thescale factor of the expanding universe incosmology^[13]
  • theacceleration inmechanics equations^[5]
  • the first constant in alinear equation
  • a constant in apolynomial
  • the unitare for area (100 m²)^[14]
  • the unit prefixatto (10⁻¹⁸)^[15]
  • the first term in asequence orseries^[16]
  • Reflectance

• B represents:
  • the digit "11" inhexadecimal^[2] and other positional numeral systems with a radix of 12 or greater^[3]
  • the second point of a triangle^[1]
  • aball (also denoted by ℬ (${\displaystyle \mathcal{B}}$) or${\displaystyle \mathbb{B}}$)^[17]
  • abasis of a vector space or of afilter (both also denoted by ℬ (${\displaystyle \mathcal{B}}$))
  • in econometrics and time-series statistics it is often used for the backshift orlag operator, the formal parameter of the lag polynomial
  • themagnetic field, denoted${\displaystyle \mathbf{\text{B}}}$ or${\displaystyle \overrightarrow{B}}$
• B with varioussubscripts represents several variations ofBrun's constant andBetti numbers; it can also be used to mean theBernoulli numbers.
  • B meson
  • Ablood type
  • Boron
  • Buoyancy
  • Bulk modulus
  • Luminance
  • Aspectral type
• b represents:
  • the second side of a triangle (opposite point B)
  • theimpact parameter in nuclearscattering
  • the second constant in alinear equation
  • usually with an index, sometimes with an arrow over it, abasis vector
  • abreadth^[10]
  • themolality of a solution^[10]
  • Bottom quark
  • Barn (10⁻²⁴ cm²)

• C represents:
  • the third point of a triangle
  • the digit "12" inhexadecimal and other positional numeral systems with a radix of 13 or greater
  • the unitcoulomb of electrical charge^[10]
  • capacitance in electrical theory
  • with indices denoting the number of combinations, a binomial coefficient
  • together with a degree symbol (°), theCelsius measurement of temperature = °C^[10]
  • thecircumference of a circle or other closed curve^[18]
  • with a subscript, acycle on that many vertices
  • with a subscript, acyclic group of that order
  • thecomplement of a set (lowercasec and the symbol ∁ are also used)
  • an arbitrarycategory
  • thenumber concentration^[10]*
  • Carbon
  • Heat capacity
  • TheC programming language
  • Cunningham correction factor
• ${\displaystyle \mathbb{C}}$ represents theset ofcomplex numbers.
• A vertically elongated C with an integer subscript n sometimes denotes the n-th coefficient of a formalpower series.
• c represents:
  • the unit prefixcenti (10⁻²)^[10]
  • theamount concentration in chemistry^[10]
  • thespeed of light in vacuum^[19]
  • the third side of a triangle (opposite corner C)
• LowercaseFraktur${\displaystyle \mathfrak{c}}$ denotes thecardinality of the set of real numbers (the "continuum"), or, equivalently, of the power set of natural numbers.
  • the third constant in alinear equation
  • a constant in apolynomial
  • Charm quark
  • Speed of sound
  • Specific heat capacity

• D represents
  • the digit "13" inhexadecimal and other positional numeral systems with a radix of 14 or greater
  • diffusion coefficient or diffusivity in dimensions of [distance²/time]
  • thedifferential operator in Euler's calculus notation
  • with a subscript, adihedral group of that order or a dihedral group on a regular polygon of that many sides, depending on the convention chosen
  • dissociation energy^[10]
  • Dimension
  • Deuterium
  • Electric displacement
  • D meson
  • Density
• d represents
  • thedifferential operator
  • the unit day of time (86,400 s)
  • the difference in an arithmetic sequence
  • a metric operator/function
  • thediameter of a circle^[10]
  • the unit prefixdeci (10⁻¹)^[10]
  • athickness^[10]
  • adistance^[10]
  • Down quark
  • Infinitesimal increment incalculus
  • Density

• E represents:
  • the digit "14" inhexadecimal and other positional numeral systems with a radix of 15 or greater
  • an exponent in decimal numbers. For example, 1.2E3 is 1.2×10³ or 1200
  • the set of edges in agraph ormatroid
  • the unit prefixexa (10¹⁸)^[10]
  • energy in physics^[10]
  • electric field denoted${\displaystyle \mathbf{\text{E}}}$ or${\displaystyle \overrightarrow{E}}$
  • electromotive force (denoted${\displaystyle \mathcal{E}}$ and measured involts), refers tovoltage
  • anevent (as in P(E), which reads "the probability P of eventE occurring")
  • in statistics, theexpected value of a random variable, sometimes as${\displaystyle \mathbb{E}}$
  • E_k representskinetic energy^[10]
  • (Arrhenius)activation energy, denotedE_a orE_A^[10]
  • ionization energy, denotedE_i^[10]
  • electron affinity, denotedE_ea^[20]
  • dissociation energy, denotedE_d^[10]
• e represents:
  • Euler's number, a transcendental number equal to 2.71828182845... which is used as the base for natural logarithms
  • a vector of unit length, especially in the direction of one of the coordinates axes
  • theelementary charge inphysics
  • anelectron, usually denoted e⁻ to distinguish against apositron e⁺
  • theeccentricity of a conic section
  • the identity element in agroup
  • In acartesian coordinate system, aunit vector in notations like${\displaystyle ({\hat{\mathbf{e}}}_x,{\hat{\mathbf{e}}}_y,{\hat{\mathbf{e}}}_z)}$, or${\displaystyle ({\hat{\mathbf{e}}}_1,{\hat{\mathbf{e}}}_2,{\hat{\mathbf{e}}}_3)}$

• F represents
  • the digit "15" inhexadecimal and other positional numeral systems with a radix of 16 or greater
  • the unitfarad of electrical capacity^[10]
  • theHelmholtz free energy of a closed thermodynamic system of constant pressure and temperature
  • together with a degree symbol (°) represents theFahrenheit measurement of temperature = °F
  • Fluorine
  • Aspectral type
• F represents
  • force in mechanics equations^[10]
  • _pF_q is ahypergeometric series
  • theprobability distributionfunction instatistics
  • aFibonacci number
  • an arbitraryfunctor
  • afield
  • anevent space sigma algebra as part of a probability space, often as${\displaystyle \mathcal{F}}$
• f represents:
  • the unit prefixfemto (10⁻¹⁵)^[10]
• f represents:
  • the generic designation of afunction
  • Friction

• G represents
  • an arbitrarygraph, as in:G(V,E)
  • an arbitrarygroup
  • the unit prefixgiga (10⁹)^[10]
  • theNewtonian constant of gravitation^[10]
  • theEinstein tensor
  • theGibbs energy
  • thecentroid of a triangle
  • Catalan's constant
  • weight measured innewtons^[10]
  • Green's function
  • aspectral type
• g represents:
  • the generic designation of a second function
  • the acceleration due togravity on Earth
  • a unit of mass, thegramme
  • Gravitational field, denotedg
  • Metric tensor (general relativity)
  • Gluon

• H represents:
  • an arbitrary subgraph
  • an arbitrary subgroup
  • aHilbert space
  • the unithenry of magnetic inductance^[10]
  • thehomology andcohomologyfunctor
  • theenthalpy
  • the (Shannon)entropy of information
  • theorthocenter of a triangle
  • a partial sum of theharmonic series
  • Auxiliary magnetic field, denoted${\displaystyle \mathit{H}}$
  • Hamiltonian in quantum mechanics
  • Hankel function
  • Heaviside step function
  • Higgs boson
  • Hydrogen
  • Set ofquaternions
  • Hat matrix
• H₀ is either theHubble constant; or theDimensionless Hubble parameter of (100 h km·s⁻¹·Mpc⁻¹, with h being the associated error.
• ${\displaystyle \mathbb{H}}$ represents thequaternions (afterWilliam Rowan Hamilton).
• ΔH^‡ represents the standardenthalpy of activation^[10] in theEyring equation.^[21]
• ℋ (${\displaystyle \mathcal{H}}$) represents the Hamiltonian inHamiltonian mechanics.
• h represents:
  • theclass number inalgebraic number theory
  • a small increment in the argument of a function
  • the unithour fortime (3600 s)
  • thePlanck constant (6.626 069(57)× 10⁻³⁴ J·s)
  • the unit prefixhecto (10²)^[10]
  • the generic designation of a third function
  • thealtitude of a triangle
  • aheight^[10]
  • Spherical Hankel function

• I represents:
  • the closed unit interval, which contains all real numbers from 0 to 1, inclusive
  • theidentity matrix
  • theIrradiance
  • themoment of inertia^[10]
  • intensity in physics, typically the vector fieldI
  • Luminous intensity, typicallyI_v
  • theincenter of a triangle
  • theelectric current^[10]
  • ionization energy, denoted I^[10]
• I represents:
  • the index of anindexed family
  • Iodine

• i represents:
  • theimaginary unit, a complex number that is the square root of −1
  • Imaginary quaternion unit
  • a subscript to denote theith term (that is, a general term or index) in a sequence or list
  • the index to the elements of a vector, written as a subscript after the vector name
  • the index to the rows of amatrix, written as the first subscript after the matrix name
  • an index of summation using thesigma notation
  • theunit vector inCartesian coordinates going in the x-direction, usually boldi

• J represents:
  • the unitjoule of energy^[10]
  • thecurrent density inelectromagnetism denoted${\displaystyle \mathit{J}}$^[10]
  • theradiosity in thermal mechanics
  • themoment of inertia^[10]
  • Total angular momentum quantum number
  • Bessel function of the first kind
  • Impulse
• J represents:
  • the scheme of adiagram in category theory
• j represents:
  • the index to the columns of amatrix, written as the second subscript after the matrix name
  • inelectrical engineering, the principal cube root of 1:${\displaystyle -\frac{1}{2}+\frac{1}{2}i\sqrt{3}}$
  • theunit vector inCartesian coordinates going in the y-direction, usually boldj
  • Electricalcurrent density
  • Spherical Bessel function of the first kind
  • Imaginary unit in electrical engineering (wherei represents current)
  • Unit vector for the second imaginary dimension in thequaternion number system (boldj)

• K represents:
  • the temperature unitkelvin^[10]
  • thefunctors ofK-theory
  • an unspecified (real) constant
  • afield in algebra
  • with a subscript, acomplete graph on that many vertices
  • the area of apolygon
  • kinetic energy^[10]
  • Kaon
  • Potassium
  • Sectional curvature
  • Aspectral type
• k represents
  • the unit prefixkilo- (10³)^[10]
  • theBoltzmann constant, often represented as k_B to avoid confusion
  • the angularwavenumber of thewave equation, the magnitude of thewave vectork
  • aninteger, e.g. adummy variable insummations, or an index of amatrix
  • an unspecified (real) constant
  • the spring constant ofHooke's law
  • the spacetimecurvature from theFriedmann equations in cosmology
  • therate constant (coefficient)^[10]
  • theunit vector inCartesian coordinates going in the z-direction, usually boldk
  • Unit vector for the third dimension in thequaternion number system (boldk)
  • Unit vector in the z direction

• L represents:
  • length, used often in quantum mechanics as the size of aninfinite square well^[10]
  • angular momentum^[10]
  • the unit of volume thelitre
  • theradiance
  • the space of all integrable real (or complex) functions
  • the space of linear maps, as inL(E,F) orL(E) =End(E)
  • thelikelihood function
  • aformal language
  • the operator creating aline graph
  • thelag operator in statistics
  • aLucas number
  • theLagrange function^[10]
  • Inductance in electromagnetism (measured inhenries)
  • Aspectral type
• l represents:
  • the unit of volume thelitre (often avoided due to confusion with the number 1 and uppercase letter I)
  • the length of a side of arectangle or acuboid (e.g. V = lwh; A = lw)
  • the last term of a sequence or series (e.g. S_n = n(a+l)/2)
  • the orbitalangular momentum quantum number^[22]
• ℒ (${\displaystyle \mathcal{L}}$) represents:
  • theLagrangian (sometimes just L)
  • exposure (in particle physics)
• ℓ represents:
  • Mean free path

• M represents:
  • amanifold
  • ametric space
  • amatroid
  • the unit prefixmega- (10⁶)^[10]
  • theMadelung constant for crystal structures held byionic bonding
  • themoment of force^[10]
    • Torque when denoted asmoment of force
  • molar mass^[10]
  • molar mass constant, denotedM_u^[10]
  • relative molecular mass, denoted M_r^[10]
  • Magnetization vector fieldM
  • Aspectral type
• m represents:
  • the number of rows in amatrix
  • atomic mass^[10]
  • atomic mass constant denotedm_u^[10]
  • theslope in a linear regression or in anyline
  • themass in mechanics equations^[10]
  • the unitmetre of length^[10]
  • the unit prefixmilli (10⁻³)^[10]
  • amedian of a triangle
  • the overallorder of reaction^[10]
  • Magnitude
  • Minute (but the SI abbreviation is "min")
  • Slope
  • Magnetic moment in amagnetization field

• N represents
  • the unitnewton of force^[10]
  • thenine-point center of a triangle
  • Bessel function of the second kind (uncommon)
  • Nitrogen
  • Normal distribution
  • Normal vector
• N represents
  • theneutron number^[10]
  • Thenumber of particles of a thermodynamical system^[23]: 57
• N_A represents theAvogadro constant
• ${\displaystyle \mathbb{N}}$ represents thenatural numbers.
• n represents
  • Aneutron, which may be shown asn,n⁰
    or¹
    ₀n
  • the unit prefixnano (10⁻⁹)^[10]
• n represents
  • the number of columns in amatrix
  • the "number of" inalgebraic equations
  • thenumber density of particles in a volume
  • the index of thenth term of a sequence or series (e.g.t_n =a + (n − 1)d)
  • theprincipal quantum number^[10]
  • the amount of a given substance^[10]
  • thenumber concentration^[10]
  • the overallorder of reaction^[10]
  • Refractive index of a material
  • Spherical Bessel function of the second kind (uncommon)
  • Aninteger

• O represents
  • the order of asymptotic behavior of a function (upper bound); seeBig O notation^[24]
  • ${\displaystyle (0,0,\dots ,0)}$ — theOrigin of the coordinate system inCartesian coordinates
  • thecircumcenter of a triangle or other cyclic polygon, or more generally the center of a circle
  • Ablood type
  • Oxygen
  • Aspectral type
• o represents
  • the order of asymptotic behavior of a function (strict upper bound); seeLittle o notation (also known as "small o notation")
  • theorder of an element in agroup
• ${\displaystyle \mathbb{O}}$ represents
  • theoctonions^[25]

• P represents:
  • thepressure in physics equations^[23]: 4
  • the unit prefixpeta (10¹⁵)^[10]
  • probability in statistics and statistical mechanics^[23]: 35
  • an arbitrary point ingeometry
  • with a subscript, apath on that many vertices
  • power, measured in watts^[10]
  • Active power in electrical engineering
  • weight measured innewtons^[10]
  • Legendre polynomial
  • Phosphorus
  • Polarization
• ${\displaystyle \mathbb{P}}$ represents
  • theprime numbers^[26]
  • Projective space^[27]
  • Projection (linear algebra)
  • aprobability (as inP(E), which reads "the probabilityP of event E happening")
• p represents
  • aprime number
  • thenumerator of a fraction
  • the unit prefixpico (10⁻¹²)^[10]
  • aproton, often p⁺ or1
    1 p
  • the linearmomentum in physics equations^[10]
  • theperimeter of a triangle or other polygon
  • generalized momentum^[10]
  • thepressure in physics equations^[10]
    • Sound pressure
  • Electric dipole moment

• Q represents:
  • the unit prefixquetta- (10³⁰)^[28]
  • heat energy^[23]: 6
  • electroweak charge, denoted Q_W^[10]
  • Reactive power in electrical engineering
  • Volumetric flow rate
• ${\displaystyle \mathbb{Q}}$ represents therational numbers^[29]
• q represents:
  • the unit prefixquecto- (10⁻³⁰)^[28]
  • a secondprime number
  • thedenominator of a fraction
  • thequotient resulting from integer division
  • thedeceleration parameter in cosmology
  • electric charge of a particle
  • ageneralized coordinate^[10]
  • Quark

• R represents:
  • the unit prefixronna- (10²⁷)^[28]
  • theRicci tensor
  • thecircumradius of a cyclic polygon such as a triangle
  • an arbitraryrelation
  • Riemann curvature tensor
  • Electrical resistance
  • Molar gas constant
• ${\displaystyle \mathbb{R}}$ represents the set of real numbers and variousalgebraic structures built upon the set of real numbers, such as${\displaystyle {\mathbb{R}}^n}$.
• r represents:
  • the unit prefixronto- (10⁻²⁷)^[28]
  • theradius of a circle or sphere^[10]
  • radial distance in apolar coordinate system orspherical coordinate system
  • theinradius of a triangle or other tangential polygon
  • the ratio of a geometric series (e.g.arⁿ⁻¹)
  • theremainder resulting from integer division
  • the separation of two objects, for example inCoulomb's law
  • aposition vector^[10]
  • the rate of concentration change of B (due tochemical reaction) denoted r_B^[30]

• S represents
  • asum
  • the unitsiemens of electric conductance^[10]
  • the unitsphere (with superscript denoting dimension)
  • thescattering matrix
  • entropy
  • action injoule-seconds^[10]
  • Apparent power in electrical engineering
  • Area
  • Spin operator
  • Sulfur
  • Symmetric group
    • with a subscript, asymmetric group on that many objects
• s represents:
  • anarclength^[10]
  • apath length^[10]
  • thedisplacement inmechanics equations
  • the unitsecond of time^[10]
  • acomplex variables = σ +it inanalytic number theory
  • thesemiperimeter of a triangle or other polygon
  • Strange quark
  • Specific entropy
• 𝒮 (${\displaystyle \mathcal{S}}$) represents a system'saction in physics
• ${\displaystyle \mathbb{S}}$ represents
  • thesedenions

• T represents:
  • thetop element of alattice
  • atree (a special kind of graph)
  • temperature in physics equations^[23]: 4
  • the unittesla of magnetic flux density^[10]
  • the unit prefixtera (10¹²)^[10]
  • thestress–energy tensor
  • tension in physics
  • an arbitrarymonad
  • the time it takes for oneoscillation^[10]
  • kinetic energy^[10]
  • Torque^[10]
  • Aspectral type
  • Tritium
  • Period, the reciprocal of frequency
• t represents:
  • time in graphs, functions or equations^[10]
  • variable ofintegration
  • a term in a sequence or series (e.g.t_n =t_n−1 + 5)
  • theimaginary part of thecomplex variables =σ +it inanalytic number theory
  • the sample statistic resulting from a Student's t-test
  • thehalf life of a quantity, denoted ast_1⁄2^[10]
  • Top quark
• ${\displaystyle \mathbb{T}}$ represents
  • thetrigintaduonions

• U represents:
  • a U-set which is aset of uniqueness
  • aunitary operator
  • in thermodynamics, theinternal energy of a system
  • aforgetful functor
  • Potential energy
  • Uranium
• U(n) represents theunitary group of degreen
• ∪ represents theunion operator
• u represents:
  • the initialvelocity in mechanics equations^[10][31]
  • Up quark

• V represents:
  • Vanadium
  • the unitvolt ofvoltage^[10]
  • the set of vertices in a graph
  • a vector space
  • potential energy^[10]
  • molar volume denoted byV_m^[10]
• v represents
  • the finalvelocity in mechanics equations^[10][31]
  • frequency,^[10] especially when referring toelectromagnetic waves^[32]
  • a specificvolume inclassical mechanics^[10]
  • the rate of concentration change of B (due tochemical reaction) denoted v_B^[30]
  • the rate of reaction based onamount concentration denoted v or v_c
  • the rate of reaction based onnumber concentration denoted v or v_C

• W represents:
  • the unitwatt of power^[10]
  • work, bothmechanical andthermodynamical^{[23]: 8–9}
  • in thermodynamics, the number of possible quantum states inBoltzmann's entropy formula
  • weight measured innewtons^[10]
  • Lambert's W function^[33]
  • Tungsten
  • W boson
  • Work function
  • Wiener process
• w represents:
  • the coordinate on the fourth axis infour-dimensional space
  • work inclassical mechanics
  • Width

• X represents
  • arandom variable
  • atriangle center
  • the first part of abipartite graph
• Ẋ represents
  • therate of change of quantity X^[10]
• x represents
  • a realized value of a random variable
  • an unknownvariable, most often (but not always) from the set ofreal numbers, while acomplex unknown would rather be calledz, and aninteger by a letter likem from the middle of the alphabet
  • the coordinate on the first orhorizontal axis in aCartesian coordinate system,^[10] or theviewport in agraph orwindow in computer graphics; theabscissa
    • Axis in the direction of travel of an aerospace vehicle (longitudinal axis)
  • amole fraction^[10]
  • Variable to be determined in analgebraic equation
  • A vector inlinear algebra

• Y represents:
  • the unit prefixyotta- (10²⁴)^[10]
  • Bessel function of the second kind
  • the second part of abipartite graph
  • Yttrium
  • Gross domestic product
• Y represents:
  • a secondrandom variable
• y represents:
  • the unit prefixyocto- (10⁻²⁴)^[10]
  • a realized value of a second random variable
  • a second unknownvariable
  • the coordinate on the second orvertical axis (backward axis in three dimensions) in aCartesian coordinate system,^[10] or in theviewport of agraph orwindow in computer graphics; theordinate
    • The port-starboard axis (transverse axis) of an aerospace vehicle
  • amole fraction^[10]

• Z represents:
  • the unit prefixzetta (10²¹)^[10]
  • theatomic number orproton number of an element in chemistry^[10]
  • a standardized normalrandom variable inprobability theory andstatistics
  • Partition function
  • in meteorology, theradar reflectivity factor
  • Electrical impedance
  • Z boson
  • Compressibility factor
• ${\displaystyle \mathbb{Z}}$ represents theintegers^[34]
• z represents:
  • the unit prefix zepto (10⁻²¹)^[10]
  • the coordinate on the third or vertical axis in threedimensional space^[10]
    • Thevertical axis oraltitude in an aerospace vehicle
  • the view depth incomputer graphics, see also "z-buffering"
  • the argument of acomplex function, or any other variable used to represent acomplex value
  • in astronomy, wavelengthredshift^[35]: 9
  • a third unknownvariable
  • thecollision frequency of A with A is denoted z_A(A)^[36]
  • thecollision frequency factor is denoted z_AB^[10]

• Blackboard bold letters used in mathematics
• Greek letters used in mathematics, science, and engineering
• List of letters used in mathematics, science, and engineering
• Mathematical Alphanumeric Symbols
• Glossary of mathematical symbols

• Elementary mathematics
• Mathematical notation
• Latin-script letters

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