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Units & Measures

The language of scales, scopes, angstroms, fractions and the magnitudes they measure.

165 terms7 shop talk8 topics
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Engineers, physicists, machinists and astronomers rely on a strict vocabulary to quantify the physical universe. This language provides the exact scale required to build a bridge, dose a medication or track a satellite. At its core is the International System of Units, providing a baseline of mutual understanding across borders and disciplines. A temperature reading in Celsius or a volume in millilitres means the exact same thing in a Tokyo laboratory as it does on a Chicago factory floor. The vocabulary of measurement is defined by absolute precision, ensuring that a physical quantity translates perfectly from a theoretical blueprint into a tangible object.

Beyond the base units, the vocabulary expands rapidly into extreme magnitudes. Metric prefixes allow scientists to scale their language to the size of their subject. A cosmologist calculating the mass of a gas giant speaks in terms of a yottagram, while a quantum physicist measuring the duration of a laser pulse works with a zeptosecond. This system of multiples and submultiples keeps the numbers manageable, preventing equations from drowning in zeros. A power plant engineer tracks thermal energy by the gigajoule, avoiding the need to write out billions of individual joules on a daily basis.

The strict rules of the laboratory do not always survive the realities of the workshop or the field. Tradespeople and technicians often rely on a parallel vocabulary of customary measures and slang. A traditional watchmaker relies on the historical ligne to size a movement, ignoring metric conventions entirely. When exact precision matters less than immediate visualization, an engineer might estimate a length in terms of a city bus. Even scientists have their inside jokes, measuring trivial distances with the attoparsec or fleeting moments with a jiffy.

Knowing when to use a precise metric term like the sverdrup to track ocean currents and when to rely on a colloquialism separates the seasoned professional from the textbook novice. The working vocabulary of measurement requires both a rigid adherence to mathematical standards and the flexibility to communicate physical reality on the job site.

Who talks like this

Physicists, metrologists, machinists, astronomers, chemists and mechanical engineers.

Start here

The ten words a newcomer to units needs first.

CelsiusA metric scale and unit of temperature where water freezes at zero and boils at one hundred.ParsecA unit of astronomical distance equal to about 3.26 light-years.GigajouleA metric unit of energy equivalent to one billion joules, often used for billing natural gas.microsecondA metric unit of time equal to one millionth of a second.BTUThe abbreviation for British thermal unit, a measure of heat energy.jiffyAn informal unit of extremely brief time, varying by technical discipline.attoparsecA humorous unit of length equal to roughly three centimetres.sverdrupA volumetric rate of flow equal to one million cubic metres per second.ligneA traditional unit of length used in watchmaking and button manufacturing.nanogramA nanogram is one billionth of a gram, used to measure trace amounts of mass.

Overheard on the job

Real-sounding lines from the floor, with every insider word decoded. Tap a highlighted word.

The laser outputs a pulse every .

Plain EnglishThe laser fires an extremely low energy burst of light every trillionth of a second.

We need a of the catalyst to achieve a reaction rate.

Plain EnglishWe require one millionth of a gram of the chemical to speed up the reaction by one thousandth of a standard unit.

The ocean current transports one , moving roughly a of water.

Plain EnglishThe current flows at one million cubic metres per second, shifting about a billion metric tonnes of water.

The gap is about an , which takes a to cross.

Plain EnglishThe distance is roughly three centimetres, and an object will traverse it in a fraction of a second.

The reactor generates a of heat, requiring a massive cooling system to keep it below a .

Plain EnglishThe power plant produces one billion joules of thermal energy and needs heavy cooling to stay under one thousand kelvins.

The old watch movement measures exactly one thick and draws a of current.

Plain EnglishThe antique timepiece mechanism is a little over two millimetres thick and uses one billionth of an amp of electricity.

The glossary

All 165 terms, grouped by topic.

165 shown

Standard SI Units

1 terms

Base and derived metric units that form the foundation of international scientific measurement.

  • Celsiusalso degrees Celsius, centigrade
    A metric scale and unit of temperature where water freezes at zero and boils at one hundred.

Metric Multiples

65 terms

Prefixes and terms used to scale up base units into massive quantities for industrial scales.

  • decaampere
    A metric unit of electrical current equal to ten amperes.
  • decagramalso dekagram, dag
    A metric unit of mass equal to ten grams, represented by the symbol dag.
  • decakatal
    A derived metric unit of catalytic activity equal to ten katals.
  • decametrealso dekameter, dam
    A metric unit of length equal to ten metres, represented by the symbol dam.
  • decasecond
    A metric unit of time measurement equal to exactly ten seconds.
  • Exajoule
    A metric unit of energy equal to one quintillion joules.
  • Exakatal
    A metric unit of catalytic activity equal to one quintillion katals.
  • Exametrealso exameter
    A massive unit of length equal to one quintillion metres, used for interstellar distances.
  • Exanewton
    An immense unit of force equal to one quintillion newtons, applied in planetary mechanics.
  • Exasecond
    A measure of time equal to one quintillion seconds, spanning tens of billions of years.
  • Gigaampere
    An SI unit of electric current equal to one billion amperes.
  • Gigagram
    A metric unit of mass equal to one billion grams, which is exactly equivalent to one kilotonne.
  • Gigajoule
    A metric unit of energy equivalent to one billion joules, often used for billing natural gas.
  • Gigakatal
    A massive unit of catalytic activity equal to one billion katals, used for industrial processes.
  • Giganewton
    A unit of force equal to one billion newtons, used to measure extreme structural and geological loads.
  • Gigasecond
    A unit of time equal to one billion seconds, which translates to just over 31.7 years.
  • hectoamperealso Hectoamp
    A metric unit of electric current equal to one hundred amperes.
  • hectobecquerel
    A metric unit of radioactivity equal to one hundred becquerels.
  • Hectogramalso hg
    A metric unit of mass equivalent to one hundred grams.
  • hectokatal
    A metric unit of catalytic activity equal to one hundred katals.
  • hectometre
    A metric unit of length equal to one hundred metres.
  • Hectopascalalso hPa
    A metric unit of pressure equal to one hundred pascals.
  • kilocandela
    A metric unit of luminous intensity equal to one thousand candelas.
  • kilodegree
    A unit of angular measurement equal to one thousand degrees.
  • kilograyalso kGy
    A metric unit of absorbed ionizing radiation dose equal to one thousand grays.
  • kilojoulealso kJ
    An SI unit of energy, work, or heat equal to 1,000 joules.
  • kilokatalalso kkat
    A metric unit of catalytic activity equal to one thousand katals.
  • kilokelvinalso kK
    A metric unit of thermodynamic temperature equal to one thousand kelvins.
  • kilometrealso kilometer, km
    A standard metric unit of length and distance equal to one thousand metres.
  • kilomolealso kmol
    A metric measure for the amount of a chemical substance that equals one thousand moles.
  • kilosecondalso ks
    A metric unit of time measurement equal to one thousand seconds.
  • Megacandelaalso Mcd
    A metric measure of luminous intensity equal to one million candelas.
  • Megagramalso Mg, metric tonne
    A metric measure of mass equal to one million grams, or one metric tonne.
  • Megahenryalso MH
    A metric measure of electrical inductance equal to one million henrys.
  • Megajoulealso MJ
    A metric measure of energy equal to one million joules.
  • megaohmalso megohm
    A unit of electrical resistance equal to one million ohms.
  • megapascalalso MPa
    A metric unit of pressure and mechanical stress equal to one million pascals.
  • Megasecondalso Ms
    A metric measure of time equal to one million seconds.
  • Petabecquerel
    A unit of radioactivity equal to one quadrillion radioactive decays per second.
  • Petagram
    A unit of mass equal to one quadrillion grams or one billion metric tonnes.
  • Petahertz
    A unit of frequency equal to one quadrillion cycles per second.
  • petajoulealso PJ
    A metric unit of energy equal to one quadrillion joules.
  • Petakelvin
    A unit of thermodynamic temperature equal to one quadrillion kelvins.
  • Petametre
    A metric unit of distance equal to one quadrillion metres, used to measure interstellar space.
  • Petasecond
    A metric unit of time equal to one quadrillion seconds, representing nearly 32 million years.
  • Petawatt
    A metric unit of power equal to one quadrillion watts, typically used to rate pulsed lasers.
  • quettagram
    A metric unit of mass equal to one nonillion grams or 10^30 grams.
  • Quettametre
    An SI unit of length equal to one nonillion metres.
  • Quettasecond
    An SI unit of time equal to one nonillion seconds.
  • ronnagram
    A metric unit of mass equal to one octillion grams or 10^27 grams.
  • Ronnametre
    An SI unit of length equal to one octillion metres.
  • Ronnasecond
    An SI unit of time equal to one octillion seconds.
  • teraampere
    A unit of electrical current equal to one trillion amperes.
  • teragram
    A unit of mass equal to one trillion grams or one million metric tonnes.
  • terajoulealso TJ
    A large unit of energy equivalent to one trillion joules of work or heat.
  • teralumenalso Tlm
    A massive measure of luminous flux equal to one trillion lumens.
  • Terametrealso Tm
    An SI unit of length equal to one trillion metres, used primarily in astronomy to measure distances within solar systems.
  • terasecond
    A metric unit of time equal to one trillion seconds, or roughly 31,700 years.
  • yottagram
    A metric unit of mass equal to one septillion grams, used for planetary bodies.
  • Yottametrealso yottameter
    A metric unit of length equal to one septillion metres.
  • Yottasecond
    A metric unit of time equal to one septillion seconds.
  • Zettagram
    A metric unit of mass equal to one sextillion grams.
  • Zettahertz
    An SI unit of frequency equal to one sextillion hertz, or 10^21 cycles per second.
  • Zettametrealso zettameter
    A metric unit of length equal to one sextillion metres.
  • zettasecond
    An SI unit of time equal to one sextillion seconds, or 10 to the 21st power.

Metric Submultiples

75 terms

Prefixes and terms that divide base units into microscopic fractions for quantum work.

  • Angstrom
    A metric unit of length equal to one ten-billionth of a meter.
  • Attoampere
    An extremely small SI unit of electric current equal to one quintillionth of an ampere.
  • Attogram
    An SI unit of mass equal to one quintillionth of a gram.
  • Attohertz
    An SI unit of frequency equal to one quintillionth of a hertz.
  • Attojoule
    An SI unit of energy equal to one quintillionth of a joule.
  • attokatal
    An SI unit of catalytic activity equal to one quintillionth of a katal.
  • attolitrealso attoliter
    A metric unit of volume equal to one quintillionth of a litre.
  • attometrealso attometer
    An SI unit of length equal to one quintillionth of a metre.
  • attosecond
    An SI unit of time equal to one quintillionth of a second.
  • attowatt
    An SI unit of power equal to one quintillionth of a watt.
  • centiamperealso cA, centiamp
    An SI unit of electric current equal to one hundredth of an ampere.
  • centigram
    A metric unit of mass equivalent to one hundredth of a gram.
  • centikatal
    A derived metric unit of catalytic activity representing one hundredth of a katal.
  • centimetre
    A base metric unit of length equal to one hundredth of a metre.
  • centimole
    A metric unit of chemical amount representing one hundredth of a mole.
  • centisecond
    A metric unit of time equal to one hundredth of a second.
  • Deciamperealso deciamp
    A metric unit of electrical current equal to one-tenth of an ampere.
  • Decigram
    A metric unit of mass equal to one-tenth of a gram.
  • Decikatal
    A metric unit of catalytic activity equal to one-tenth of a katal.
  • Decilitre
    A metric unit of volume equal to one-tenth of a litre.
  • Decimetre
    A metric unit of length equal to one-tenth of a metre.
  • Decisecond
    A metric unit of time equal to one-tenth of a second.
  • femtobecquerel
    A unit of radioactive decay equal to one quadrillionth of a becquerel.
  • femtobel
    A logarithmic unit of relative power equal to one quadrillionth of a bel.
  • femtocandela
    A unit of luminous intensity equal to one quadrillionth of a candela.
  • femtocoulomb
    A unit of electric charge equal to one quadrillionth of a coulomb.
  • Femtofarad
    A unit of electrical capacitance equal to one quadrillionth of a farad.
  • femtogram
    A unit of mass equal to one quadrillionth of a gram.
  • femtojoule
    A unit of energy equal to one quadrillionth of a joule.
  • Femtokatal
    A metric measurement of enzymatic rate equivalent to one quadrillionth of a katal.
  • Femtometrealso fermi
    An SI unit of length equal to one quadrillionth of a metre.
  • Femtosecond
    A unit of time equal to one quadrillionth of a second, used to measure ultrafast laser pulses.
  • Microgramalso μg, mcg
    A metric mass measurement that represents a millionth part of a single gram.
  • Microkatalalso μkat
    A metric measure of catalytic activity equal to one millionth of a katal.
  • microkelvin
    A metric unit of thermodynamic temperature equal to one millionth of a kelvin.
  • micromole
    A metric unit of amount of substance equal to one millionth of a mole.
  • microsecond
    A metric unit of time equal to one millionth of a second.
  • microtesla
    A metric unit of magnetic flux density equal to one millionth of a tesla.
  • milligramalso mg
    A metric unit of mass equal to one thousandth of a gram.
  • millikatal
    A metric unit of catalytic activity equal to one thousandth of a katal.
  • millisecond
    A metric unit of time equal to one thousandth of a second.
  • nano-ampalso nanoamp, nA
    A nano-amp is one billionth of an ampere, used to measure extremely small electrical currents. Shop talk
  • nano-faradalso nanofarad, nF
    A nano-farad is one billionth of a farad, a standard measure of electrical capacitance. Shop talk
  • nano-ohmalso nΩ
    A unit of electrical resistance equal to one billionth of an ohm.
  • nanoamperealso nA
    A nanoampere is one billionth of an ampere, the standard SI unit for very small electrical currents.
  • nanogramalso ng
    A nanogram is one billionth of a gram, used to measure trace amounts of mass.
  • nanojoulealso nJ, nano-joule
    A nanojoule is one billionth of a joule, the standard SI unit for very small amounts of energy.
  • nanokatalalso nkat
    A nanokatal is one billionth of a katal, measuring trace levels of catalytic activity.
  • Nanokelvin
    A unit of thermodynamic temperature equal to one billionth of a kelvin.
  • Nanomole
    A unit of chemical amount equal to one billionth of a mole.
  • Nanosecond
    A unit of time equal to one billionth of a second.
  • Nanovoltalso nano-volt, nV
    A unit of electrical potential equal to one billionth of a volt.
  • Picoamperealso picoamp
    A unit of electrical current equal to one trillionth of an ampere.
  • picogramalso pg
    A metric unit of mass equal to one trillionth of a gram.
  • Picokatal
    A unit of catalytic activity equal to one trillionth of a katal.
  • Picometre
    A unit of length equal to one trillionth of a metre.
  • Piconewton
    A unit of force equal to one trillionth of a newton.
  • Picosecond
    A unit of time equal to one trillionth of a second.
  • Picosiemens
    A unit of electrical conductance equal to one trillionth of a siemens.
  • Quectogram
    An SI unit of mass equal to one nonillionth of a gram.
  • Quectosecond
    An SI unit of time equal to one nonillionth of a second.
  • rontogram
    An incredibly small mass unit equal to one octillionth of a gram.
  • rontosecond
    A minuscule unit of time equivalent to one octillionth of a second.
  • yoctoampere
    An SI unit of electrical current equal to one septillionth of an ampere.
  • yoctogram
    An SI unit of mass equal to one septillionth of a gram.
  • yoctokatal
    An SI unit of catalytic activity equal to one septillionth of a katal.
  • yoctoliteralso yoctolitre
    An SI unit of volume equal to one septillionth of a liter.
  • yoctometre
    An SI unit of length equal to one septillionth of a metre.
  • yoctomole
    A metric measurement representing one septillionth of a mole.
  • yoctosecond
    An SI unit of time equal to one septillionth of a second.
  • Zeptogram
    A metric unit of mass equal to one sextillionth of a gram.
  • Zeptojoule
    A metric unit of energy equal to one sextillionth of a joule.
  • Zeptoliteralso zeptolitre
    A metric unit of volume equal to one sextillionth of a liter.
  • Zeptometrealso zeptometer
    A metric unit of length equal to one sextillionth of a metre.
  • Zeptosecond
    A metric unit of time equal to one sextillionth of a second.

Imperial & Customary

6 terms

Traditional weights and measures still used in regional trades and legacy engineering.

  • Acre-foot
    A customary volume measure used in large-scale water management, equal to the amount of water needed to cover one acre to a depth of one foot.
  • BTUalso British thermal unit
    The abbreviation for British thermal unit, a measure of heat energy.
  • horsepower-houralso hp-hr
    A customary unit of energy equal to the work done by one horsepower over one hour.
  • Imperialalso imperial system, British imperial
    A system of weights and measures established by the British Empire.
  • Milalso thou
    A unit of length equal to one thousandth of an inch.
  • MPGalso miles per gallon
    A measure of vehicle fuel efficiency showing how far a vehicle can travel on one gallon of fuel.

Historic & Obsolete

6 terms

Abandoned measurement systems and archaic units preserved in specialized crafts.

  • Abfarad
    An obsolete unit of capacitance equal to one billion standard farads.
  • Abmho
    A historic unit of electrical conductance equal to one billion siemens.
  • Abvolt
    An obsolete unit of electromotive force equal to ten nanovolts.
  • Abwatt
    An electromagnetic power measure equivalent to a ten-millionth fraction of a standard watt.
  • lignealso line
    A traditional unit of length used in watchmaking and button manufacturing.
  • Pollum
    A historic Indian unit of weight equivalent to roughly one and a fifth ounces.

Astronomical & Geographic

4 terms

Massive scales used to calculate planetary masses, ocean currents and interstellar distances.

  • Lunar distancealso LD
    An astronomical measure based on the average gap between the Earth and the Moon.
  • milliarcsecondalso mas
    A unit of angular measurement equal to one thousandth of an arcsecond.
  • Parsec
    A unit of astronomical distance equal to about 3.26 light-years.
  • sverdrupalso Sv
    A volumetric rate of flow equal to one million cubic metres per second.

Informal & Slang

5 terms

Colloquial comparisons and humorous units used by technicians to visualize abstract quantities.

  • attoparsec
    A humorous unit of length equal to roughly three centimetres. Shop talk
  • City bus
    A colloquial unit of length or mass used to help visualize large industrial objects. Shop talk
  • jiffy
    An informal unit of extremely brief time, varying by technical discipline. Shop talk
  • London bus
    An informal British unit of length or volume used to help people visualize large objects. Shop talk
  • School bus
    An informal unit of length representing about 40 feet or 12 metres. Shop talk

Symbols & Abbreviations

3 terms

The standard shorthand and letters used in formulas, blueprints and technical documentation.

  • Mlalso mL, millilitre
    The standard symbol for the millilitre, a metric unit of fluid volume.
  • PPT
    A dimensionless measure of concentration denoting parts per trillion.
  • Salso scruple
    The traditional abbreviation for a scruple in the apothecaries' weight system.

Questions people ask

What is the difference between a megagram and a metric tonne?

There is no physical difference between the two terms. A megagram is the strict SI term for one million grams. A metric tonne is the exact same mass, but it is a non SI term accepted for use with the metric system. Industry and commerce heavily favor the metric tonne, while scientific literature sometimes prefers the megagram.

How big is a yottagram compared to a ronnagram?

A ronnagram is one thousand times larger than a yottagram. The yotta prefix denotes a factor of one septillion, or ten to the twenty fourth power. The ronna prefix denotes a factor of one octillion, or ten to the twenty seventh power. Astronomers use these massive scales to quantify the mass of planets, moons and stars.

What does the prefix femto mean in measurement?

The prefix femto indicates a factor of one quadrillionth, or ten to the negative fifteenth power. Scientists use it to measure extremely small quantities in quantum mechanics and particle physics. A femtosecond is one quadrillionth of a second, which is the timescale on which chemical reactions occur and atoms vibrate.

Why do scientists use the parsec instead of light years?

The parsec is directly derived from observable geometry rather than the speed of light. It represents the distance at which the radius of the Earth orbit subtends an angle of one arcsecond. This makes the parsec highly practical for astronomers calculating distances using trigonometric parallax, whereas the light year is mostly used in popular science communication.

What does a sverdrup measure?

A sverdrup measures the volumetric rate of fluid flow, specifically for ocean currents. One sverdrup equals one million cubic metres of water moving per second. Oceanographers use this unit to quantify massive global water movements, such as the Gulf Stream, without having to write out excessively large numbers in their calculations.

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