How Many? A Dictionary of Units of Measurement
© Russ Rowlett and the University of North Carolina at Chapel Hill

Table of Contents
About the Dictionary
Using the Dictionary

K

K
an informal abbreviation for one thousand used in expressions where the unit is understood, such as "10K run" (10 kilometers) or "700K disk" (700 kilobytes or kibibytes). Note that "K" is also the symbol for the kelvin (see below) and is often used as a symbol for the karat. Also note that the symbol for the metric prefix kilo- (1000) is actually k-, not K-. In computer science, K often represents 210 = 1024 (see below under kibi- and kilo-).
kaf
a symbol for 1000 acre feet. This symbol is commonly used in reservoir management in the U.S. 1 kaf = about 1.2335 million cubic meters.
kairi
the Japanese name for the nautical mile.
kanal
a traditional unit of land area in Pakistan, equal to 20 marlas. Under British rule the marla and kanal were standardized so that the kanal equals exactly 605 square yards or 1/8 acre; this is equivalent to about 505.857 square meters.
kappland
a traditional unit of land area in Sweden. The kappland is equal to 1/32 tunnland or 1750 square Stockholm feet (kvadratfot); this is equivalent to 154.26 square meters or about 184.50 square yards.
karat (kt) [1]
a traditional unit of mass for precious stones, now spelled carat in both Britain and the U.S.
karat (kt or K) [2]
a traditional measure of proportion equal to 1/24, used by U.S. jewelers to express the purity of gold alloys. Thus "14-karat gold" is legally required to be at least 14/24, or 58.3%, gold. In Britain this unit is spelled carat, like the weight unit for diamonds and other precious stones. American jewelers apparently spell the unit of gold purity with the "k" and the weight unit with the "c" in order to distinguish more clearly between them. (In German, both units are spelled with the "k".)
katal (kat)
a unit of catalytic activity used especially in the chemistry of enzymes. A catalyst is a substance that starts or speeds a chemical reaction. Enzymes are proteins that act as catalysts within the bodies of living plants and animals. A catalyst has an activity of one katal if it enables a reaction to proceed at the rate of one mole per second. The unit, pronounced "cattle," was added to the International System at the 21st General Conference of Weights and Measures in October 1999.
kati
a traditional Malaysian unit of weight, usually spelled catty in English.
kattha or katta
a traditional unit of land area in South Asia, equal to 20 dhurs or 1/20 bigha. Like the bigha, the kattha varied in size from one region to another. In Nepal, where the unit is still in use, the kattha equals about 338 square meters or 442 square yards.
kayser (K)
a CGS unit used to measure light and other electromagnetic waves. The "wave number" in kaysers equals the number of wavelengths per centimeter; thus 1 kayser equals 100 per meter (m-1). The unit honors J. H. G. Kayser (1853-1940), who compiled a giant atlas of chemical spectra. The unit is often abbreviated K, although this conflicts with the symbol for the kelvin.
kbp
a symbol for 1000 base pairs, used in biochemistry and genetics. As is well known, DNA has the form of a double helix, with bases on one strand paired with bases on the other strand. Thus the length of a segment or fragment of DNA is measured by the number of base pairs.
kBtu
a symbol for 1000 British thermal units. This unit of energy equals about 1.055 megajoules (MJ) or 0.2931 kilowatt hour (kWh).
kcmil
a symbol for 1000 circular mils, a unit of area equal to about 0.5067 square millimeter commonly used in stating wire gauges.
keddah
a traditional Egyptian unit of liquid volume also used in other parts of the Middle East. The keddah is equal to about 2.0625 liter (about 2.18 U.S. liquid quarts or 1.815 British Imperial quarts).
keel
a traditional British unit of weight for coal. After considerable variation, the keel of coal was standardized in 1695 as 21.2 long tons, or 47 488 pounds (21.5402 metric tons). This is the approximate weight of coal carried at that time by barges on the river Tyne in northern England; the barges were also called keels, from the Dutch word kiel for such a ship.
keg [1]
a traditional unit of volume or quantity, varying with the item contained in the keg. A keg of herring, for example, contains 60 fish. A keg of wine is frequently 12 U.S. gallons (about 45.42 liters), and a keg of beer is 1/2 barrel or 15.5 U.S. gallons (about 58.67 liters). "Keg" comes from an old Norse word for a small barrel.
keg [2]
a traditional unit of weight for nails. A keg of nails weighs 100 pounds and thus has a mass of about 45.359 kilograms.
kelvin (K)
the SI base unit of temperature, previously called the degree Kelvin (°K). One kelvin represents the same temperature difference as one degree Celsius. In 1967 the General Conference on Weights and Measures defined the temperature of the triple point of water (the temperature at which water exists simultaneously in the gaseous, liquid, and solid states) to be exactly 273.16 kelvins. Since this temperature is also equal to 0.01 °C, the temperature in kelvins is always equal to 273.15 plus the temperature in degrees Celsius. The kelvin equals exactly 1.8 degrees Fahrenheit. The unit is named for the British mathematician and physicist William Thomson (1824-1907), later known as Lord Kelvin after he was named Baron Kelvin of Largs. He is best remembered for his pioneering work on the physics of heat, but he was also a strong advocate of the metric system; his support helped establish the now-familiar electrical units such as the ohm, volt, and farad.
ken
a traditional Japanese unit of length comparable to the English fathom. The ken equals 6 shaku, which is about 1.818 meters (5.965 feet). The ken is the length of a traditional tatami mat. At sea, this unit is also called the hiro.
kerat
a traditional Middle Eastern unit of length, equal to about 9/8 inch or 2.86 centimeters. The unit has the same Arabic root as the carat or karat.
key
slang for kilo, meaning kilogram.
kgm
an incorrect symbol for the kilogram (see below). The correct symbol is kg. In engineering, "kgm" is sometimes used to distinguish "kilogram mass" from "kilogram force" (kgf). This practice is not recommended.
kgr
another incorrect (but fairly common) symbol for the kilogram. The proper symbol is kg.
kgsc
a non-standard symbol for kilograms (of force) per square centimeter.
kibi- (Ki-)
a binary prefix meaning 210 = 1024. This prefix, adopted by the International Electrotechnical Commission in 1998, was supposed to replace kilo- for binary applications in computer science. Thus 1024 bytes of storage is officially a kibibyte, not a kilobyte. However, computer professionals generally dislike this unit (they say it sounds like a cat food) so the ambiguity in the size of a kilobyte persists. The prefix is a contraction of "kilobinary." The symbol Ki-, rather than ki-, was chosen for uniformity with the other binary prefixes (Mi-, Gi-, etc.).
kilderkin
an old British unit of volume equal to 1/2 barrel or 2 firkins. Based on the current British barrel, this would be 18 (Imperial) gallons, which is about 2.9 cubic feet or 78 liters. Older kilderkins were generally in the range of 16-18 gallons. The word comes from a Dutch word for a small cask.
kilo
a common informal name for a kilogram.
kilo- (k-) [1]
a metric prefix meaning 1000. The prefix is a modification of chilioi, the Greek word for a thousand.
kilo- (k-) [2]
in measuring the memory of a computer, the prefix kilo- often means 210 = 1024 instead of 1000. By a 1998 resolution of the International Electrotechnical Commission, the new prefix kibi- (Ki-) should replace kilo- for 210. However, this doesn't seem to be happening.
kiloampere (kA)
a unit of electric current equal to 1000 amperes.
kilobar (kbar or kb)
a metric unit of pressure, used particularly in industrial applications and in geology for measuring high pressures. The kilobar equals 1000 bars, 100 megapascals, or about 14 503 pounds per square inch. (Note: in the investment world a kilobar is a bar of gold, silver, or platinum weighing 1 kilogram.)
kilobase (kb)
a unit of genetic information equal to the information carried by 1000 pairs of the base units in the double-helix of DNA; also used as a unit of relative distance equal to the length of a strand of DNA containing 1000 base pairs.
kilobecquerel (kBq)
a unit of radioactivity equal to 1000 atomic disintegrations per second or 27.027 nanocuries (nCi).
kilobit (kbit or kb)
a unit of information equal to 1000 bits, or, in some cases, equal to 1024 bits or 128 bytes. The larger unit is now supposed to be called a kibibit.
kilobit per second (kbps, kb/s)
a unit of data transmission rate equal to 1000 bits per second. The symbol kb/s is preferable to kbps for this unit.
kilobyte (kB)
a unit of information equal to 1000 bytes. As a unit of computer storage, however, the kilobyte is usually equal to 1024 bytes, although this should now be called a kibibyte.
kilocalorie (kcal)
an ambiguous metric unit of energy. The ambiguity arises because there are two "calories" in common use, identified in this dictionary as the calorie (the small or gram calorie equal to 4.1868 kilojoules) and the Calorie (the large or kilogram calorie equal to 4.1868 megajoules). The term kilocalorie properly means 1000 calories, which is the same as 1 Calorie. In other words, "kilocalorie" is the correct name for the unit known in nutrition simply as the "calorie."
kilocurie (kCi)
a unit of radioactivity equal to 1000 curies or 37 terabecquerels (TBq), that is, 37 trillion atomic disintegrations per second. The strength of the powerful radiation sources used in cancer therapy are customarily stated in kilocuries.
kilocycle (kc)
1000 cycles; a term sometimes used as an informal name for the kilohertz.
kilocycle per second (kc/s)
an older name for the kilohertz.
kilodalton (kDa)
a unit of mass equal to 1000 atomic mass units. See dalton.
kiloelectronvolt (keV)
a unit of work or energy used in physics, equal to 1000 electronvolts.
kilofoot (kft)
a traditional unit of distance equal to 1000 feet or exactly 304.8 meters. This odd combination of a metric prefix and an English unit is used in telecommunications to describe cable lengths and transmission distances.
kilogauss (kGs)
a metric unit of magnetic flux density equal to 1000 gauss or 0.1 tesla. The strength of industrial magnets and solenoids is often expressed in kilogauss, although this unit is being replaced gradually by the tesla.
kilogram (kg) [1]
the base unit of mass in the SI and MKS versions of the metric system. The kilogram is defined as the mass of the standard kilogram, a platinum-iridium bar in the custody of the International Bureau of Weights and Measures (BIPM) near Paris, France. Copies of this bar are kept by the standards agencies of all the major industrial nations, including the U.S. National Institute of Standards and Technology (NIST). One kilogram equals exactly 1000 grams, or about 2.204 622 6 pounds. By design, this is approximately the mass of a liter of water.
kilogram (kg) [2]
a unit of force; see below under kilogram force.
kilogram calorie (kcal or kgcal)
the "large calorie" or "food calorie" used in nutrition, equal to 1000 ordinary ("gram") calories. The correct name for this unit is kilocalorie.
kilogram force (kgf)
a unit of force equal to the gravitational force on a mass of one kilogram. One kilogram of force equals 9.806 65 newtons, or 2.204 622 6 pounds of force in the traditional English system. Using this unit revives the old confusion between mass and weight, one of the worst features of traditional measurement systems, so it is really a very bad idea. However, kilograms of force have been used rather frequently in engineering and physics. This unit is also called the kilopond.
kilogram meter (kgf·m or kg·m) [1]
a metric unit of work or energy equal to 9.806 65 joules (J). This is the work done by one kilogram of force (see below) acting through a distance of one meter.
kilogram meter (kgf·m or kg·m) [2]
a metric unit of torque equal to 9.806 65 newton meters (N·m).
kilogram mole, kilogram molecule, kilogram molecular weight (kgmol or kgmole)
various older names for a unit of the amount of a chemical compound. One kilogram mole of a compound is the number of kilograms of the compound equal to the molecular weight of a molecule of that compound measured in atomic mass units. The correct name for this unit is the kilomole (kmol).
kilogram (force) per square centimeter (kgf/cm2 or kg/cm2 or kgsc)
a common metric unit of pressure equal to 98.0665 kilopascals (see below) or about 14.2234 pounds per square inch (lbf/in2 or psi). Similarly, one kilogram force per square meter is equal to 9.806 65 pascals.
kilogram weight (kgf)
a kilogram force (see above).
kilohertz (kHz)
a common unit of frequency equal to 1000 per second or 1 per millisecond. AM radio stations have signal frequencies measured in kilohertz.
kilojoule (kJ)
a common metric unit of work or energy, comparable to the British thermal unit (Btu). In fact, one kilojoule equals approximately 0.947 817 Btu. In other energy units, the kilojoule is also equivalent to 0.238 846 kilocalories, 0.277 778 watt hour, or 737.562 foot-pounds in the traditional English system.
kilokibibyte
a unit of computer memory equal to exactly 1 024 000 bytes. Storage on floppy disks is traditionally stated in multiples of this unit, which has usually been called a "megabyte." But a megabyte should be 1 000 000 bytes, or with a binary understanding it should be 220 = 1 048 576 bytes, and this unit doesn't fit either convention.
kiloline
a metric unit of magnetic flux, equal to 1000 lines [2] or 10 microwebers.
kiloliter (kl or kL)
a metric unit of volume. The kiloliter is identical to the cubic meter: it equals about 35.3147 ft3, 1.307 95 yd3, 264.17 U.S. gallons, 219.99 British Imperial gallons, 7.497 U.S. bushels, or 6.049 British Imperial bushels.
kilomega- (kM-)
an obsolete metric prefix denoting 109 (1 U.S. billion). This prefix has been replaced by giga- (G-).
kilometer (km)
a common metric unit of length or distance. One kilometer equals exactly 1000 meters, about 0.621 371 19 mile, 1093.6133 yards, or 3280.8399 feet. Oddly, higher multiples of the meter are rarely used; even the distances to the farthest galaxies are usually measured in kilometers. The unit is sometimes pronounced with the accent on the first syllable (similar to the pronunciation of other metric units using kilo-) and sometimes on the second (helping to distinguish it from other metric units using kilo-). Both pronunciations are acceptable; there are no official pronunciations for SI units.
kilometer per hour (km/h)
a common metric unit of speed or velocity. 1 km/h is equal to 5/18 meter per second, 0.621 371 19 miles per hour or 0.911 344 42 feet per second. The only correct symbol for this unit is km/h; variations such as kmph or kph should not be used.
kilometer per liter (km/L or km/l)
a fairly common unit of fuel consumption rate for vehicles. Outside the U.S., the official measurement of fuel efficiency is usually liters per 100 kilometers, but many people prefer to express the measurement in kilometers per liter. One kilometer per liter is equal to about 2.352 146 miles per U.S. gallon or 2.824 809 miles per Imperial gallon. A consumption rate of x kilometers per liter is equivalent to 100/x liters per 100 kilometers.
kilomole (kmol)
a unit of amount of substance equal to 1000 moles. One kilomole of a compound is the number of kilograms of the compound equal to the molecular weight of a molecule of that compound in atomic mass units. The kilomole was formerly called the kilogram mole.
kilonewton (kN)
a common metric unit of force, the kilonewton equals 1000 newtons; it is a force that will accelerate a mass of 1 metric ton at the rate of 1 meter per second per second. One kilonewton equals 101.972 kilograms of force, 224.809 pounds of force or 7233.01 poundals.
kilohm or kiloohm
a unit of electric resistance equal to 1000 ohms. The simplified spelling kilohm is approved by the Institute of Electrical and Electronics Engineers (IEEE).
kilo-oersted (kOe)
a CGS unit of magnetic field strength equivalent in MKS units to 79 577.472 ampere-turns per meter. The unit, used for stating the field strengths of industrial magnets, is almost always spelled with the hyphen.
kiloparsec (kpc)
a unit of distance used in astronomy, the kiloparsec equals 1000 parsecs, 3261.631 light years, 3.085 678 x 1016 kilometers, or about 19.18 quadrillion miles. The Solar System is located about 8 kiloparsecs from the center of the Milky Way galaxy.
kilopascal (kPa)
a common metric unit of pressure. One kilopascal equals 1000 pascals (Pa), 10 millibars (mb), or about 0.145 038 pounds per square inch (lbf/in2 or psi), 20.8855 pounds per square foot, 7.502 millimeters of mercury (mm Hg), 0.2953 inches of mercury (in Hg), 4.015 inches of water column (in WC), or 0.3346 foot of head (ft hd).
kilopond (kp)
another name for the kilogram of force (kgf) (see above).
kilorad (krad)
a common unit of radiation dose equal to 1000 rads, 10 grays, or 10 joules of energy per kilogram of mass.
kilosecond (ks or ksec)
a unit of time equal to 1000 seconds (16 minutes 40 seconds). Although it is never used in ordinary life, the kilosecond has many uses in science. One day is equal to 86.4 kiloseconds.
kiloton (kt or KT or kton) [1]
an ambiguous unit of mass, ambiguous because it may refer to 1000 U.S. tons (907 185 kilograms), 1000 British tons (1 016 047 kilograms), or 1000 metric tons (1 million kilograms, or 1 gigagram). To reduce this confusion, the metric unit should be written kilotonne.
kiloton (kt or KT or kton) [2]
a unit of explosive energy equal to 1012 thermochemical calories (or one teracalorie). This is approximately the energy released by exploding 1000 U.S. tons (2 million pounds) of TNT. The kiloton is equal to exactly 4.184 terajoules (4.184 x 1012 joules) or about 4 billion Btu.
kilovolt (kV)
a common unit of electric potential equal to 1000 volts. Electric distribution lines operate at potentials of anywhere from several to several hundred kilovolts.
kilovolt ampere (kV·A)
a common unit of load in power engineering, equal to 1000 volt amperes.
kilowatt (kW)
a common metric unit of power, equivalent to 1000 watts, about 1.341 022 horsepower, or 737.562 foot-pounds per second.
kilowatt hour (kW·h or KWH or kw hr)
a commercial unit of electric energy. One kilowatt hour represents the amount of energy delivered at a rate of 1000 watts over a period of one hour. Since the watt is 1 joule/sec and there are 3600 seconds in an hour, the kilowatt hour is equivalent to exactly 3.6 megajoules of energy, or about 3412.141 Btu, 859.846 (kilogram) Calories, or about 2.655 million foot pounds.
kilowatt year (kW·yr)
a commercial unit of electric energy. One kilowatt year represents the amount of energy delivered at a rate of 1000 watts over a period of one year. This equals 8760 kilowatt hours for an ordinary (365 day) year or 8784 kilowatt hours for a leap year. For greater accuracy, it's best to use 365.25 days per year; with this definition, the kilowatt year is exactly 8766 kilowatt hours or 31.5576 gigajoules; this is about 1.2463 million Btu or 969.8 million foot-pounds.
kiloyard (kyd)
a traditional unit of distance equal to 1000 yards (exactly 914.4 meters). This unit is used in the U.S., British, and Commonwealth navies in describing ship distances and target ranges.
kiloyear (kyr)
a unit of time equal to 1000 years, commonly used in archaeology, paleontology, climatology, and related sciences. Of course, a kiloyear is the same as a millennium.
kin
the Japanese version of the catty, a common weight unit of the Far East. The Japanese identified this unit with a traditional unit equal to about 1.323 pounds or almost exactly 600 grams; this is about 0.75% smaller than the Chinese catty.
kip [1]
an informal unit of force, sometimes used by engineers to express the amount of weight borne by a structure. One kip equals 1000 pounds (453.59 kilograms) of force or about 4.4482 kilonewtons. The name of the unit is an abbreviation of "kilopound."
kip [2]
a symbol for 1000 inch pounds, used as a unit of energy or torque. In this usage one kip is equal to 83.333 foot pounds (lbf·ft), 112.985 joules (J), or, for torque, 112.985 newton meters (N·m).
kip [3]
an old English word for a bundle of hides. It was sometimes used as a unit of quantity, usually equal to 50.
klafter [1]
a traditional unit of distance in German-speaking countries, comparable to the English fathom. The Austrian klafter is equal to 1.8965 meters (6.22 feet). In Switzerland the klafter was brought into the metric system at exactly 1.8 meters (5.9055 feet). This unit is also called the faden.
klafter [2]
a traditional German unit of volume for stacked firewood, comparable to the English cord. A klafter of wood was generally 1 klafter tall and 1 klafter long, but there was less agreement on its width, that is, the length of the logs. A common width was 3 fuss or 0.5 klafter, making the volume about 3.41 steres (cubic meters) or 0.941 cord by the Viennese definition, 3.34 steres or 0.921 cord in northern Germany.
klick, klik
see click.
kmph
a common but incorrect symbol for kilometers per hour. The correct symbol is km/h.
km/t
a symbol for "kilometer per time," used on road signs in Scandinavia, especially Norway, for kilometers per hour.
Knoop hardness (HK or KHN)
a measure of the hardness of a metal introduced by Knoop in 1939. The Knoop test is similar to the Vickers test in that a diamond penetrator is used to indent the sample being tested, but it uses a rhombohedral diamond rather than a pyramidal diamond point. It is similar to the Rockwell test in that the hardness measure is the depth of the penetration rather than its area. The result is measured in kilograms of force per square millimeter but should be stated as an empirical measurement, without units.
knot (kn or kt) [1]
a unit of velocity equal to one nautical mile per hour. Knots are customarily used to express speeds at sea, including the speed of the ship as well as the speeds of the wind and of the current. The word comes from the former method of measuring a ship's speed, which involved use of a knotted cord called the log line. One knot equals about 1.1508 miles per hour, exactly 1.852 kilometers per hour, or 0.5143 meters per second. Since kt is the established symbol for the kilotonne, kn is the best choice as a symbol for the knot.
knot [2]
an informal unit of distance equal to the nautical mile.
köddi
a traditional Arabic unit of volume, equal to about 4/3 British Imperial gallon or 7.58 liters.
koku
a traditional Japanese unit of volume, equal to about 180.391 liters (39.68 British Imperial gallons or 6.37 cubic feet). The unit originated as an estimate of the amount of rice needed to feed a person for a year.
kommerzlast
German for "commercial load," now interpreted as a metric unit equal to exactly 3 tonnes (about 6613.9 pounds).
kon
Korean name for the catty.
koyan
a Far Eastern unit of weight equal to 4000 catty or 5333.33 pounds (8/3 short ton).
kph
a common but incorrect symbol for kilometers per hour. The correct symbol is km/h.
krina
a traditional unit of volume in Bulgaria, now expressed in the metric system as being equal to exactly 20 liters (4.40 British Imperial gallons or 5.28 U.S. liquid gallons).
Krügerl or Krügel
a common unit of volume for beer in Austria, equal to 1/2 liter. The name of the unit is related to Krug, a jug or tankard.
ksf, ksi
symbol for kips (kilopounds) per square foot or per square inch, traditional engineering units of pressure or stress. 1 ksf = 47.880 257 kilopascals (kPa) and 1 ksi = 6.894 757 megapascals (MPa). These units are often used to express the strength of materials (meaning the maximum pressure the material can resist).
ksym/s
a unit of radio transmission rate equal to 1000 symbols per second.
kulmet
a traditional Latvian unit of volume equal to about 10.93 liters (2.40 British Imperial gallons or 2.89 U.S. liquid gallons). A similar Estonian unit, the külimet, equals about 11.48 liters (2.53 British Imperial gallons or 3.03 U.S. liquid gallons).
kunitz or Kunitz unit
a unit used in biochemistry to describe the concentration or activity of the enzyme ribonuclease, which attacks ribonucleic acid (RNA). The action of the enzyme causes an increase in the absorbance of ultraviolet light. One kunitz is the concentration of the enzyme causing an increase in absorbance at a wavelength of 260 nm by 0.001 per mL of enzyme when acting upon highly polymerized DNA at 25 C and pH 5.0 under specified conditions. The unit's name recognizes the Russian-American biochemist M. Kunitz, who proposed the standard test in 1946.
kvadrat-
Scandinavian prefix meaning "square." In particular, a kvadratmeter is a square meter. The prefix is common to Danish, Norwegian, and Swedish.
kwan
a traditional Japanese unit of weight equal to 6.25 kin (see above), which is about 8.27 pounds or 3.75 kilograms.
kya
a common abbreviation (in English speaking countries) for "thousand years ago." The "k" is the metric symbol for kilo- (1000).
kyu
a metric unit of distance used in typography and graphic design. The kyu, originally written Q, is equal to exactly 0.25 millimeter, about 0.71 point [2], or about 14.173 twips. The spelling "kyu" seems to have been introduced by the software company Macromedia.
Kz
an improper symbol sometimes used mistakenly for the kilohertz (kHz).

 

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October 1, 2002