In the

natural sciences Natural science or empirical science is one of the branches of science concerned with the description, understanding and prediction of natural phenomena, based on empirical evidence from observation and experimentation. Mechanisms such as peer ...

, including

physiology Physiology (; ) is the science, scientific study of function (biology), functions and mechanism (biology), mechanisms in a life, living system. As a branches of science, subdiscipline of biology, physiology focuses on how organisms, organ syst ...

and

engineering Engineering is the practice of using natural science, mathematics, and the engineering design process to Problem solving#Engineering, solve problems within technology, increase efficiency and productivity, and improve Systems engineering, s ...

, a specific quantity generally refers to an

intensive quantity Physical or chemical properties of materials and systems can often be categorized as being either intensive or extensive, according to how the property changes when the size (or extent) of the system changes. The terms "intensive and extensive ...

obtained by the ratio of an

extensive quantity Physical or chemical properties of materials and systems can often be categorized as being either intensive or extensive, according to how the property changes when the size (or extent) of the system changes. The terms "intensive and extensive ...

of interest by another extensive quantity (usually

mass Mass is an Intrinsic and extrinsic properties, intrinsic property of a physical body, body. It was traditionally believed to be related to the physical quantity, quantity of matter in a body, until the discovery of the atom and particle physi ...

volume Volume is a measure of regions in three-dimensional space. It is often quantified numerically using SI derived units (such as the cubic metre and litre) or by various imperial or US customary units (such as the gallon, quart, cubic inch) ...

). If mass is the divisor quantity, the specific quantity is a ''massic quantity''. If volume is the divisor quantity, the specific quantity is a ''volumic quantity''. For example, massic leaf area is

leaf A leaf (: leaves) is a principal appendage of the plant stem, stem of a vascular plant, usually borne laterally above ground and specialized for photosynthesis. Leaves are collectively called foliage, as in "autumn foliage", while the leav ...

area divided by leaf mass and volumic leaf area is leaf area divided by leaf volume.

Derived SI unit SI derived units are units of measurement derived from the seven SI base units specified by the International System of Units (SI). They can be expressed as a product (or ratio) of one or more of the base units, possibly scaled by an appropriat ...

s involve reciprocal kilogram (kg⁻¹), e.g.,

square metre The square metre ( international spelling as used by the International Bureau of Weights and Measures) or square meter ( American spelling) is the unit of area in the International System of Units (SI) with symbol m2. It is the area of a square ...

per kilogram (m²kg⁻¹). Another kind of specific quantity, termed ''named specific quantity'', is a generalization of the original concept. The divisor quantity is not restricted to mass, and name of the divisor is usually placed before "specific" in the full term (e.g., "

thrust-specific fuel consumption Thrust-specific fuel consumption (TSFC) is the fuel efficiency of an engine design with respect to thrust output. TSFC may also be thought of as fuel consumption (grams/second) per unit of thrust (newtons, or N), hence ''thrust-specific''. This fig ...

"). Named and unnamed specific quantities are given for the terms below.

List

Mass-specific quantities

Per unit of mass (short form of ''mass-specific''): *

Specific absorption rate Specific absorption rate (SAR) is a measure of the rate at which energy is absorbed per unit mass by a human body when exposed to a radio frequency (RF) electromagnetic field. It is defined as the power absorbed per mass of tissue and has unit ...

, power absorbed per unit mass of tissue at a given frequency *

Specific activity Specific activity (symbol ''a'') is the activity per unit mass of a radionuclide and is a physical property of that radionuclide. It is usually given in units of becquerel per kilogram (Bq/kg), but another commonly used unit of specific activi ...

, radioactivity in becquerels per unit mass *

Specific energy Specific energy or massic energy is energy per unit mass. It is also sometimes called gravimetric energy density, which is not to be confused with energy density, which is defined as energy per unit volume. It is used to quantify, for example, st ...

, defined as energy per unit mass **

Specific internal energy The internal energy of a thermodynamic system is the energy of the system as a state function, measured as the quantity of energy necessary to bring the system from its standard internal state to its present internal state of interest, account ...

internal energy The internal energy of a thermodynamic system is the energy of the system as a state function, measured as the quantity of energy necessary to bring the system from its standard internal state to its present internal state of interest, accoun ...

per unit mass **

Specific kinetic energy In physics, particularly in mechanics, specific kinetic energy is a fundamental concept that refers to the kinetic energy per unit mass of a body or system of bodies in motion. The specific kinetic energy of a system is a crucial parameter in un ...

, kinetic energy of an object per unit of mass *

Specific enthalpy Enthalpy () is the sum of a thermodynamic system's internal energy and the product of its pressure and volume. It is a state function in thermodynamics used in many measurements in chemical, biological, and physical systems at a constant extern ...

, enthalpy per unit mass *

Specific enzyme activity Enzyme assays are laboratory methods for measuring enzymatic activity. They are vital for the study of enzyme kinetics and enzyme inhibition. Enzyme units The quantity or concentration of an enzyme can be expressed in molar amounts, as with any ...

, activity per milligram of total protein *

Specific force Specific force (SF) is a mass-specific quantity defined as the quotient of force per unit mass. :\mathrm = F / m It is a physical quantity of kind acceleration, with dimension of length per time squared and units of metre per second squared (m· ...

, defined as the non-gravitational force per unit mass *

Specific growth rate Relative growth rate (RGR) is growth rate relative to size - that is, a rate of growth per unit time, as a proportion of its size at that moment in time. It is also called the exponential growth rate, or the continuous growth rate. Rationale RGR ...

, increase in cell mass per unit cell mass per unit time *

Specific heat capacity In thermodynamics, the specific heat capacity (symbol ) of a substance is the amount of heat that must be added to one unit of mass of the substance in order to cause an increase of one unit in temperature. It is also referred to as massic heat ...

, heat capacity per unit mass, unless another unit is named, such as mole-specific heat capacity, or volume-specific heat capacity *

Specific latent heat Latent heat (also known as latent energy or heat of transformation) is energy released or absorbed, by a body or a thermodynamic system, during a constant-temperature process—usually a first-order phase transition, like melting or condensation. ...

, latent heat per unit mass *

Specific leaf area Specific leaf area (SLA) is the ratio of leaf area to leaf dry mass. The inverse of SLA is Leaf Mass per Area (LMA). Rationale Specific leaf area is a ratio indicating how much leaf area a plant builds with a given amount of leaf biomass: SLA \ = ...

, leaf area per unit dry leaf mass *

Specific modulus Specific modulus is a materials property consisting of the elastic modulus per mass density of a material. It is also known as the stiffness to weight ratio or specific stiffness. High specific modulus materials find wide application in aerospace a ...

, a materials property consisting of the elastic modulus per mass density of a material *

Specific orbital energy In the gravitational two-body problem, the specific orbital energy \varepsilon (or specific ''vis-viva'' energy) of two orbiting bodies is the constant quotient of their mechanical energy (the sum of their mutual potential energy, \varepsilon ...

, orbital energy per unit mass *

Specific power Power-to-weight ratio (PWR, also called specific power, or power-to-mass ratio) is a calculation commonly applied to engines and mobile power sources to enable the comparison of one unit or design to another. Power-to-weight ratio is a measurement ...

, per unit of mass (or volume or area) *

Specific relative angular momentum In celestial mechanics, the specific relative angular momentum (often denoted \vec or \mathbf) of a body is the angular momentum of that body divided by its mass. In the case of two orbiting bodies it is the vector product of their relative positi ...

, of two orbiting bodies is angular momentum per unit reduced mass, or the vector product of the relative position and the relative velocity *

Specific surface area Specific surface area (SSA) is a property of solids defined as the total surface area (SA) of a material per unit mass, (with units of m2/kg or m2/g). Alternatively, it may be defined as SA per solid or bulk volume (units of m2/m3 or m−1). I ...

, per unit of mass, volume, or cross-sectional area *

Specific volume In thermodynamics, the specific volume of a substance (symbol: , nu) is the quotient of the substance's volume () to its mass (): :\nu = \frac It is a mass-specific intrinsic property of the substance. It is the reciprocal of density (rho) ...

, volume per unit mass, i.e. the reciprocal of density

Geometry specific quantities

Volume-specific quantity, the quotient of a physical quantity and volume ("per unit volume"), also called ''volumic'' quantities: * Specific mass, actually meaning ''volume-specific'' mass, or mass per unit volume; same as

density Density (volumetric mass density or specific mass) is the ratio of a substance's mass to its volume. The symbol most often used for density is ''ρ'' (the lower case Greek letter rho), although the Latin letter ''D'' (or ''d'') can also be u ...

. *

Specific weight Specific may refer to: * Specificity (disambiguation) * Specific, a cure or therapy for a specific illness Law * Specific deterrence, focussed on an individual * Specific finding, intermediate verdict used by a jury in determining the fin ...

, weight per unit volume *

Charge density In electromagnetism, charge density is the amount of electric charge per unit length, surface area, or volume. Volume charge density (symbolized by the Greek letter ρ) is the quantity of charge per unit volume, measured in the SI system in co ...

, the electric charge per volume *

Energy density In physics, energy density is the quotient between the amount of energy stored in a given system or contained in a given region of space and the volume of the system or region considered. Often only the ''useful'' or extractable energy is measure ...

, potential energy per unit volume *

Force density In fluid mechanics, the force density is the negative gradient of pressure. It has the physical dimensions of force per unit volume. Force density is a vector field representing the flux density of the hydrostatic force within the bulk of a fl ...

, force per unit volume *

Power density Power density, defined as the amount of power (the time rate of energy transfer) per unit volume, is a critical parameter used across a spectrum of scientific and engineering disciplines. This metric, typically denoted in watts per cubic meter ...

, power per unit volume * Particle density (particle count), number of particles per unit volume Area-specific quantity, the quotient of a physical quantity and area ("per unit area"), also called ''areic'' quantities: *

Current density In electromagnetism, current density is the amount of charge per unit time that flows through a unit area of a chosen cross section. The current density vector is defined as a vector whose magnitude is the electric current per cross-sectional ...

, the ratio of electric current to area *

Surface power density In physics and engineering, surface power density is power per unit area. Applications * The intensity of electromagnetic radiation can be expressed in W/m2. An example of such a quantity is the solar constant. * Wind turbines are often compared ...

, power per unit area *

Specific surface energy In surface science, surface energy (also interfacial free energy or surface free energy) quantifies the disruption of intermolecular bonds that occurs when a surface is created. In solid-state physics, surfaces must be intrinsically less Gibbs fr ...

, free energy per unit surface area Length-specific quantity, the quotient of a physical quantity and length ("per unit length"), also called ''lineic'' quantities: * Linear charge density, charge per unit length * Linear mass density, mass per unit length *

Linear number density In mathematics, the term ''linear'' is used in two distinct senses for two different properties: * linearity of a '' function'' (or '' mapping''); * linearity of a ''polynomial''. An example of a linear function is the function defined by f(x)= ...

, number of entities per unit length * reciprocal length quantities

Other specific quantities

In chemistry: * Molar quantities *

Concentration In chemistry, concentration is the abundance of a constituent divided by the total volume of a mixture. Several types of mathematical description can be distinguished: '' mass concentration'', '' molar concentration'', '' number concentration'', ...

Per unit of other types. The dividing unit is sometimes added before the term "specific", and sometimes omitted. *

Brake-specific fuel consumption Brake-specific fuel consumption (BSFC) is a measure of the fuel efficiency of any prime mover that burns fuel and produces rotational, or shaft power. It is typically used for comparing the efficiency of internal combustion engines with a shaft out ...

, fuel consumption per unit of braking power *

Thrust-specific fuel consumption Thrust-specific fuel consumption (TSFC) is the fuel efficiency of an engine design with respect to thrust output. TSFC may also be thought of as fuel consumption (grams/second) per unit of thrust (newtons, or N), hence ''thrust-specific''. This fig ...

, fuel consumption per unit of thrust * Specific acid catalysis, in which the reaction rate is proportional to the concentration of the protonated solvent molecules *

Specific acoustic impedance Acoustic impedance and specific acoustic impedance are measures of the opposition that a system presents to the acoustic flow resulting from an acoustic pressure applied to the system. The SI unit of acoustic impedance is the pascal-second per cu ...

, ratio of sound pressure ''p'' to particle speed at a single frequency * Specific capacity of a water well, quantity of water produced per (length) unit of drawdown * Specific conductance, conductance per meter. Identical to

electrical conductivity Electrical resistivity (also called volume resistivity or specific electrical resistance) is a fundamental specific property of a material that measures its electrical resistance or how strongly it resists electric current. A low resistivity in ...

Specific detectivity Specific detectivity, or ''D*'', for a photodetector is a figure of merit used to characterize performance, equal to the reciprocal of noise-equivalent power (NEP), normalized per square root of the sensor's area and frequency bandwidth (reciproc ...

of a photodetector * Specific fuel consumption (disambiguation). Fuel consumption per unit thrust, or per unit power. Type defined as above. *

Specific gas constant The molar gas constant (also known as the gas constant, universal gas constant, or ideal gas constant) is denoted by the symbol or . It is the molar equivalent to the Boltzmann constant, expressed in units of energy per temperature increment pe ...

, per molar mass * Specific heat of vaporization,

enthalpy of vaporization In thermodynamics, the enthalpy of vaporization (symbol ), also known as the (latent) heat of vaporization or heat of evaporation, is the amount of energy (enthalpy) that must be added to a liquid substance to transform a quantity of that sub ...

, vaporizing heat per mole *

Specific humidity Humidity is the concentration of water vapor present in the air. Water vapor, the gaseous state of water, is generally invisible to the human eye. Humidity indicates the likelihood for precipitation, dew, or fog to be present. Humidity dep ...

, mass of water vapor per unit mass dry air *

Specific impulse Specific impulse (usually abbreviated ) is a measure of how efficiently a reaction mass engine, such as a rocket engine, rocket using propellant or a jet engine using fuel, generates thrust. In general, this is a ratio of the ''Impulse (physics), ...

, impulse (momentum change) per unit of propellant (either per unit of propellant mass, or per unit of propellant by Earth-weight) * Specific melting heat,

enthalpy of fusion In thermodynamics, the enthalpy of fusion of a substance, also known as (latent) heat of fusion, is the change in its enthalpy resulting from providing energy, typically heat, to a specific quantity of the substance to change its state from a ...

; melting heat per mole *

, elastic modulus per mass density * Specific resistance (disambiguation), several scientific meanings *

Specific rotation In chemistry, specific rotation ( �'') is a property of a chiral chemical compound. It is defined as the change in orientation of monochromatic plane-polarized light, per unit distance–concentration product, as the light passes through a sampl ...

of a chemical, angle of optical rotation α of plane-polarized light per standard sample with a path length of one decimeter and a sample concentration of one gram per millilitre * Specific speed, unitless figure of merit used to classify pump impellers (pump-specific) and turbines (turbine-specific). Ratio of performance against reference pump that needs one unit of speed to pump one unit volume per one unit hydraulic head pressure. For a turbine, it is performance measured against a reference turbine that develops one unit of power per one unit speed per one unit of hydraulic head. *

Specific storage In the field of hydrogeology, ''storage properties'' are physical properties that characterize the capacity of an aquifer to release groundwater. These properties are storativity (S), specific storage (Ss) and specific yield (Sy). According to ' ...

specific yield In the field of hydrogeology, ''storage properties'' are physical properties that characterize the capacity of an aquifer to release groundwater. These properties are storativity (S), specific storage (Ss) and specific yield (Sy). According to '' ...

, and specific capacity, quantify the capacity of an aquifer to release groundwater from storage per unit decline in hydraulic head pressure *

Specific strength The specific strength is a material's (or muscle's) strength (force per unit area at failure) divided by its density. It is also known as the strength-to-weight ratio or strength/weight ratio or strength-to-mass ratio. In fiber or textile applic ...

, material strength (pressure required at failure) per unit material density *

, per unit of mass, volume, or cross-sectional area * Specific thrust, thrust per unit air intake rate

Usage

;Reference tables: Specific properties are often used in reference tables as a means of recording material data in a manner that is independent of size or mass. This allows the data to be broadly applied while keeping the table compact. ;Ranking, classifying, and comparing: Specific properties are useful for making comparisons about one attribute while cancelling out the effect of variations in another attribute. For instance, steel alloys are typically stronger than aluminum alloys but are also much denser. Greater strength allows less metal to be used, which makes the choice between the two metals less than obvious. To simplify the comparison, one would compare the

specific strength The specific strength is a material's (or muscle's) strength (force per unit area at failure) divided by its density. It is also known as the strength-to-weight ratio or strength/weight ratio or strength-to-mass ratio. In fiber or textile applic ...

(strength to weight ratio) of the two metals. A more everyday example relates to grocery shopping: a 2 kg package sells for a higher price than 1 kg package of the same foodstuff, but what matters is the "specific price", commonly called the unit cost (cost in currency units per kilogram). ;Mnemonics and qualitative reasoning: In many instances, specific properties are more intuitive or are easier to remember than the original properties, whether in SI or imperial units. For instance, it is easier to conceptualize an acceleration of 2''g'' than an acceleration of 19.6 meters per second squared.

References