Measuring instrument

A measuring instrument is a device to measure a physical quantity. In the physical sciences, quality assurance, and engineering, measurement is the activity of obtaining and comparing physical quantities of real-world objects and events. Established standard objects and events are used as units, and the process of measurement gives a number relating the item under study and the referenced unit of measurement. Measuring instruments, and formal test methods which define the instrument's use, are the means by which these relations of numbers are obtained. All measuring instruments are subject to varying degrees of instrument error and measurement uncertainty. These instruments may range from simple objects such as rulers and stopwatches to electron microscopes and particle accelerators. Virtual instrumentation is widely used in the development of modern measuring instruments.

A measuring instrument for lengths: a typical tape measure with both metric and imperial units and two US pennies for comparison
A measuring instrument for radio waves: the 64-meter radio telescope at Parkes Observatory, Australia, as seen in 1969, when it was used to receive live televised video from Apollo 11


Watch, a time measurement device

In the past, a common time measuring instrument was the sundial. Today, the usual measuring instruments for time are clocks and watches. For highly accurate measurement of time an atomic clock is used. Stopwatches are also used to measure time in some sports.


Measuring instruments in fiction: Captain Nemo and Professor Aronnax contemplating thermometers, barometers, clocks, etc. in Jules Verne's 1869-1870 science fiction novel Twenty Thousand Leagues Under the Sea
Fun measuring instruments: a Love Meter and strength tester machine at a Framingham, Massachusetts rest stop.

Energy is measured by an energy meter. Examples of energy meters include:

Electricity meter

An electricity meter measures energy directly in kilowatt-hours.

Gas meter

A gas meter measures energy indirectly by recording the volume of gas used. This figure can then be converted to a measure of energy by multiplying it by the calorific value of the gas.

Power (flux of energy)

A physical system that exchanges energy may be described by the amount of energy exchanged per time-interval, also called power or flux of energy.

  • (see any measurement device for power below)

For the ranges of power-values see: Orders of magnitude (power).


Action describes energy summed up over the time a process lasts (time integral over energy). Its dimension is the same as that of an angular momentum.


Length (distance)

  • Length, distance, or range meter

For the ranges of length-values see: Orders of magnitude (length)


For the ranges of area-values see: Orders of magnitude (area)


A measuring cup, a common instrument used to measure volume.

If the mass density of a solid is known, weighing allows to calculate the volume.

For the ranges of volume-values see: Orders of magnitude (volume)


Orientation in three-dimensional space

See also the section about navigation below.




This includes basic quantities found in classical- and continuum mechanics; but strives to exclude temperature-related questions or quantities.

Mass- or volume flow measurement

Speed or velocity (flux of length)

For the ranges of speed-values see: Orders of magnitude (speed)



A pair of scales: An instrument for measuring mass in a force field by balancing forces.

For the ranges of mass-values see: Orders of magnitude (mass)

Linear momentum

Force (flux of linear momentum)

Measuring absolute pressure in an accelerated reference frame: The principle of a mercury (Hg) barometer in the gravitational field of the earth.

Pressure (flux density of linear momentum)

For the ranges of pressure-values see: Orders of magnitude (pressure)

Angular velocity or rotations per time unit

For the value-ranges of angular velocity see: Orders of magnitude (angular velocity)

For the ranges of frequency see: Orders of magnitude (frequency)


Energy carried by mechanical quantities, mechanical work

Electricity, electronics, and electrical engineering

Considerations related to electric charge dominate electricity and electronics. Electrical charges interact via a field. That field is called electric field.If the charge doesn't move. If the charge moves, thus realizing an electric current, especially in an electrically neutral conductor, that field is called magnetic. Electricity can be given a quality — a potential. And electricity has a substance-like property, the electric charge. Energy (or power) in elementary electrodynamics is calculated by multiplying the potential by the amount of charge (or current) found at that potential: potential times charge (or current). (See Classical electromagnetism and Covariant formulation of classical electromagnetism)

An instrument for detecting net charges, the electroscope.

Electric charge

For the ranges of charge values see: Orders of magnitude (charge)

Electric current (current of charge)

Voltage (electric potential difference)

Electric resistance, electrical conductance, and electrical conductivity

Electric capacitance

Electric inductance

Energy carried by electricity or electric energy

Power carried by electricity (current of energy)

Electric field (negative gradient of electric potential, voltage per length)

  • Field mill

Magnetic field

See also the relevant section in the article about the magnetic field.

For the ranges of magnetic field see: Orders of magnitude (magnetic field)

Combination instruments

  • Multimeter, combines the functions of ammeter, voltmeter, and ohmmeter as a minimum.
  • LCR meter, combines the functions of ohmmeter, capacitance meter, and inductance meter. Also called component bridge due to the bridge circuit method of measurement.


Temperature-related considerations dominate thermodynamics. There are two distinct thermal properties: A thermal potential — the temperature. For example: A glowing coal has a different thermal quality than a non-glowing one.

And a substance-like property, — the entropy; for example: One glowing coal won't heat a pot of water, but a hundred will.

Energy in thermodynamics is calculated by multiplying the thermal potential by the amount of entropy found at that potential: temperature times entropy.

Entropy can be created by friction but not annihilated.

Amount of substance (or mole number)

A physical quantity introduced in chemistry; usually determined indirectly. If mass and substance type of the sample are known, then atomic- or molecular masses (taken from a periodic table, masses measured by mass spectrometry) give direct access to the value of the amount of substance. (See also Molar mass.) If specific molar values are given, then the amount of substance of a given sample may be determined by measuring volume, mass, or concentration. See also the subsection below about the measurement of the boiling point.
  • Gas collecting tube gases


Imaging technology

See also Temperature measurement and Category:Thermometers. More technically related may be seen thermal analysis methods in materials science.

For the ranges of temperature-values see: Orders of magnitude (temperature)

Energy carried by entropy or thermal energy

An active calorimeter lacking a temperature measurement device.

This includes thermal mass or temperature coefficient of energy, reaction energy, heat flow, ... Calorimeters are called passive if gauged to measure emerging energy carried by entropy, for example from chemical reactions. Calorimeters are called active or heated if they heat the sample, or reformulated: if they are gauged to fill the sample with a defined amount of entropy.

See also Calorimeter or Calorimetry


Entropy is accessible indirectly by measurement of energy and temperature.

Entropy transfer

Phase change calorimeter's energy value divided by absolute temperature give the entropy exchanged. Phase changes produce no entropy and therefore offer themselves as an entropy measurement concept. Thus entropy values occur indirectly by processing energy measurements at defined temperatures, without producing entropy.

Entropy content

The given sample is cooled down to (almost) absolute zero (for example by submerging the sample in liquid helium). At absolute zero temperature any sample is assumed to contain no entropy (see Third law of thermodynamics for further information). Then the following two active calorimeter types can be used to fill the sample with entropy until the desired temperature has been reached: (see also Thermodynamic databases for pure substances)

Entropy production

Processes transferring energy from a non-thermal carrier to heat as a carrier do produce entropy (Example: mechanical/electrical friction, established by Count Rumford). Either the produced entropy or heat are measured (calorimetry) or the transferred energy of the non-thermal carrier may be measured.

  • calorimeter
  • (any device for measuring the work which will or would eventually be converted to heat and the ambient temperature)

Entropy lowering its temperature—without losing energy—produces entropy (Example: Heat conduction in an isolated rod; "thermal friction").

  • calorimeter

Temperature coefficient of energy or "heat capacity"

Concerning a given sample, a proportionality factor relating temperature change and energy carried by heat. If the sample is a gas, then this coefficient depends significantly on being measured at constant volume or at constant pressure. (The terminology preference in the heading indicates that the classical use of heat bars it from having substance-like properties.)

Specific temperature coefficient of energy or "specific heat capacity"

The temperature coefficient of energy divided by a substance-like quantity (amount of substance, mass, volume) describing the sample. Usually calculated from measurements by a division or could be measured directly using a unit amount of that sample.

For the ranges of specific heat capacities see: Orders of magnitude (specific heat capacity)

Coefficient of thermal expansion

Melting temperature (of a solid)

Boiling temperature (of a liquid)

See also Thermal analysis, Heat.

More on continuum mechanics

This includes mostly instruments which measure macroscopic properties of matter: In the fields of solid-state physics; in condensed matter physics which considers solids, liquids, and in-betweens exhibiting for example viscoelastic behavior. Furthermore, fluid mechanics, where liquids, gases, plasmas, and in-betweens like supercritical fluids are studied.


This refers to particle density of fluids and compact(ed) solids like crystals, in contrast to bulk density of grainy or porous solids.

  • Aerometer liquids
  • Dasymeter gases
  • Gas collecting tube gases
  • Hydrometer liquids
  • Pycnometer liquids
  • Resonant frequency and damping analyser (RFDA) solids

For the ranges of density-values see: Orders of magnitude (density)

Hardness of a solid

Shape and surface of a solid

  • Holographic interferometer
  • Laser produced speckle pattern analysed.
  • Resonant frequency and damping analyser (RFDA)
  • Tribometer

Deformation of condensed matter

Elasticity of a solid (elastic moduli)

  • Resonant frequency and damping analyser (RFDA), using the impulse excitation technique: A small mechanical impulse causes the sample to vibrate. The vibration depends on elastic properties, density, geometry, and inner structures (lattice or fissures).

Plasticity of a solid

  • Cam plastometer
  • Plastometer
Measurement results (a) brittle (b) ductile with breaking point (c) ductile without breaking point.

Tensile strength, ductility, or malleability of a solid

Granularity of a solid or of a suspension

  • Grindometer

Viscosity of a fluid

Optical activity

Surface tension of liquids

  • Tensiometer

Imaging technology

  • Tomograph, device and method for non-destructive analysis of multiple measurements done on a geometric object, for producing 2- or 3-dimensional images, representing the inner structure of that geometric object.
  • Wind tunnel

This section and the following sections include instruments from the wide field of Category:Materials science, materials science.

More on electric properties of condensed matter, gas

The electrochemical cell: A device for measuring substance potentials.

Permittivity, relative static permittivity, (dielectric constant), or electric susceptibility

Such measurements also allow to access values of molecular dipoles.

Magnetic susceptibility or magnetization

For other methods see the section in the article about magnetic susceptibility.

See also Category:Electric and magnetic fields in matter

Substance potential or chemical potential or molar Gibbs energy

Phase conversions like changes of aggregate state, chemical reactions or nuclear reactions transmuting substances, from reactants into products, or diffusion through membranes have an overall energy balance. Especially at constant pressure and constant temperature, molar energy balances define the notion of a substance potential or chemical potential or molar Gibbs energy, which gives the energetic information about whether the process is possible or not - in a closed system.

Energy balances that include entropy consist of two parts: A balance that accounts for the changed entropy content of the substances, and another one that accounts for the energy freed or taken by that reaction itself, the Gibbs energy change. The sum of reaction energy and energy associated to the change of entropy content is also called enthalpy. Often the whole enthalpy is carried by entropy and thus measurable calorimetrically.

For standard conditions in chemical reactions either molar entropy content and molar Gibbs energy with respect to some chosen zero point are tabulated. Or molar entropy content and molar enthalpy with respect to some chosen zero are tabulated. (See Standard enthalpy change of formation and Standard molar entropy)

The substance potential of a redox reaction is usually determined electrochemically current-free using reversible cells.

Other values may be determined indirectly by calorimetry. Also by analyzing phase-diagrams.

Sub-microstructural properties of condensed matter, gas

Crystal structure

Imaging technology, microscope

(See also Spectroscopy and List of materials analysis methods.)

Rays ("waves" and "particles")

Sound, compression waves in matter

Microphones in general, sometimes their sensitivity is increased by the reflection- and concentration principle realized in acoustic mirrors.

Sound pressure

A device for unmixing sun-light: the prism.

Light and radiation without a rest mass, non-ionizing

(for lux meter, see the section about human senses and human body)

See also Category:Optical devices

Photon polarization

Pressure (current density of linear momentum)

  • Nichols radiometer

Radiant flux

The measure of the total power of light emitted.

  • Integrating sphere for measuring the total radiant flux of a light source
A Cathode-ray tube

Cathode rays

Atom polarization and electron polarization

Another visualization of the electromagnetic spectrum.

Ionizing radiation

Ionizing radiation includes rays of "particles" as well as rays of "waves". Especially X-rays and gamma rays transfer enough energy in non-thermal, (single-) collision processes to separate electron(s) from an atom.

A cloud chamber detecting alpha-rays.

Particle and ray flux

Identification and content

This could include chemical substances, rays of any kind, elementary particles, and quasiparticles. Many measurement devices outside this section may be used or at least become part of an identification process. For identification and content concerning chemical substances, see also Analytical chemistry, List of chemical analysis methods, and List of materials analysis methods.

Substance content in mixtures, substance identification

pH: Concentration of protons in a solution


Human senses and human body

Brightness: photometry

Photometry is the measurement of light in terms of its perceived brightness to the human eye. Photometric quantities derive from analogous radiometric quantities by weighting the contribution of each wavelength by a luminosity function that models the eye's spectral sensitivity. For the ranges of possible values, see the orders of magnitude in: illuminance, luminance, and luminous flux.

  • Photometers of various kinds:
  • Integrating sphere for collecting the total luminous flux of a light source, which can then be measured by a photometer
  • Densitometer for measuring the degree to which a photographic material reflects or transmits light

Color: colorimetry

  • Tristimulus colorimeter for quantifying colors and calibrating an imaging workflow

Radar brightness: radiometry

Synthetic Aperture Radar (SAR) instruments measure radar brightness, Radar Cross Section (RCS), which is a function of the reflectivity and moisture of imaged objects at wavelengths which are too long to be perceived by the human eye. Black pixels mean no reflectivity (e.g. water surfaces), white pixels mean high reflectivity (e.g. urban areas). Colored pixels can be obtained by combining three gray-scaled images which usually interpret the polarization of electromagnetic waves. The combination R-G-B = HH-HV-VV combines radar images of waves sent and received horizontally (HH), sent horizontally and received vertically (HV) and sent and received vertically (VV). The calibration of such instruments is done by imaging objects (calibration targets) whose radar brightness is known.

Loudness in phon


Body temperature or core temperature

Circulatory system (mainly heart and blood vessels for distributing substances fast)

Blood-related parameters are listed in a blood test.

Respiratory system (lung and airways controlling the breathing process)

A spirometer, inhaling into pipe a fills volume b, the rest balances forces.

Concentration or partial pressure of carbon dioxide in the respiratory gases

Nervous system (nerves transmitting and processing information electrically)

power, work of muscles

  • Ergometer

metabolic system

Medical imaging

An echocardiogram processed into a three dimensional representation.

See also: Category:Physiological instruments and Category:Medical testing equipment.


See also Category:Meteorological instrumentation and equipment.

See also Category:Navigational equipment and Category:Navigation. See also Surveying instruments.


See also Astronomical instruments and Category:Astronomical observatories.


Some instruments, such as telescopes and sea navigation instruments, have had military applications for many centuries. However, the role of instruments in military affairs rose exponentially with the development of technology via applied science, which began in the mid-19th century and has continued through the present day. Military instruments as a class draw on most of the categories of instrument described throughout this article, such as navigation, astronomy, optics, and imaging, and the kinetics of moving objects. Common abstract themes that unite military instruments are seeing into the distance, seeing in the dark, knowing an object's geographic location, and knowing and controlling a moving object's path and destination. Special features of these instruments may include ease of use, speed, reliability, and accuracy.

Uncategorized, specialized, or generalized application

Alphabetical listing

Instrument Quantity measured
alcoholmeteralcoholic strength of liquid
ammeterelectric current
astrolabelatitude and altitude of celestial bodies
barkometertanning liquors used in tanning leather
barometerair pressure
bettsometerintegrity of fabric coverings on aircraft
bevametermechanical properties of soil
bolometerelectromagnetic radiation
Brannock Devicemeasuring shoe size
breathalyzerbreath alcohol content
calorimeterheat of chemical reactions
cathetometervertical distances
ceilometerheight of a cloud base
chronometer or clocktime
clap-o-metervolume of applause
compassdirection of North
Coulombmeterelectrostatic charge of a material
creepmeterslow surface displacement of an active geologic fault in the earth
corratorcorrosion rate
declinometermagnetic declination
densimeterspecific gravity of liquids
densitometerdegree of darkness in photographic or semitransparent material
diffractometerstructure of crystals
dilatometervolume changes caused by a physical or chemical process
disdrometersize, speed, and velocity of raindrops
dosimeterexposure to hazards, especially radiation; radiation of item
drumometer amount of drum strokes over time
dumpy levelhorizontal levels, polar angle
dynamometerforce, torque, or power
electricity meterelectrical energy used
electrometerelectric charge
electronic tunerpitch of musical notes
ellipsometerrefractive index, dielectric function, thickness of thin films
eudiometerchange in volume of a gas mixture following combustion
evaporimeterrate of evaporation
fathometerocean depth
feeler gaugegap widths
forward looking infrared (FLIR)detects infrared energy (heat)converts it into an electronic signal, which is then processed to produce a thermal image on a video monitor and perform temperature calculations.
framing squareright angles in construction
frequency counterfrequency of alternating current
fuel gaugefuel levels
gas pycnometervolume and density of solids
geiger counterionizing radiation (alpha, beta, gamma, etc.)
glucometerblood glucose (diabetes)
heliometervariation of the sun's diameter
hourmeterelapsed machine hours
hydrometerspecific gravity of liquids (density of liquids)
inclinometerangle of a slope
interferometerwave interference
infrared thermometerheat radiated
katharometercomposition of gases
lactometerspecific gravity of milk
light meterlight (in photography)
linear position transducerspeed of movement
load cellmeasurement of force
lux meterintensity of light
magnetometerstrength of magnetic fields
manometerpressure of gas
mass flow metermass flow rate of a fluid travelling through a tube
mass spectrometermasses of ions, used to identify chemical substances through their mass spectra
measuring cupliquid and dry goods
measuring cylindervolume
measuring spoona spoon used to measure an amount of an ingredient, either liquid or dry
meggerelectrical insulation
mercury barometerAtmospheric pressure
micrometersmall distances
multimeterelectrical potential, resistance, and current
nephoscopeto measure the speed and direction of clouds
nephelometerparticle in a liquid
odometerdistance travelled
ohmmeterelectrical resistance
opisometerlengths of arbitrary curved lines
orchidometertesticle size in male humans
osmometerosmotic strength of a solution, colloid, or compound matter of an object
parking metercollects moneys for vehicle parking rights in a zone for a limited time
pH meterpH (chemical acidity/basicity of a solution)
photometerilluminance or irradiance
polarimeterrotation of polarized light
potentiometervoltage (term is also used to refer to a variable resistor)
profilometersurface roughness
pycnometerfluid density
pyranometersolar radiation
pyrheliometerdirect solar insolation
pyrometerhigh temperatures
quadratpercentage cover of a certain species
quartz crystal microbalancethickness of deposited thin films
rain gaugemeasuring of rain
radiometerradiant flux of electromagnetic radiation
refractometerindex of refraction
rheometerresponse to applied forces
rotameterpressure of a liquid or gas in a closed tube
rulerfor measuring length
saccharometeramount of sugar in a solution
seismometerseismic waves (for example, earthquakes)
sextantlocation on earth's surface (used in naval navigation)
spectrometerproperties of light
spectrophotometerintensity of light as a function of wavelength
speedometerspeed, velocity of a vehicle
spirometerthe lung capacity
spherometerradius of a sphere
sphygmomanometerblood pressure
stadimeterobject range
strainmeterseismic strain
SWR meterstanding wave ratio
Synthetic Aperture Radarreflectivity and moisture
tachometerrevolutions per minute, rate of blood flow, speed of aeroplanes
taximeterdistance travelled, displacement
tensiometersurface tension of a liquid
theodoliteangle, in the horizontal and vertical planes
tiltmeterminor changes to the Earth
universal measuring machinegeometric locations
vacuum gaugevery low pressure
viscometerviscosity of a fluid
voltmeterelectric potential, voltage
VU metervolume unit
wattmeterelectrical power
weighing scaleweight
wind vanewind direction

See also


The alternate spelling "-metre" is never used when referring to a measuring device.


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