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The ton is a unit of measure. It has a long history and has acquired a number of meanings and uses over the years. It is used principally as a unit of mass. Its original use as a measurement of volume has continued in the capacity of cargo ships and in terms such as the freight ton. It can also be used as a measure of energy, for truck classification, or as a colloquial term.

Unit of measurement real scalar quantity, defined and adopted by convention, with which any other quantity of the same kind can be compared to express the ratio of the two quantities as a number (International vocabulary of metrology)

A unit of measurement is a definite magnitude of a quantity, defined and adopted by convention or by law, that is used as a standard for measurement of the same kind of quantity. Any other quantity of that kind can be expressed as a multiple of the unit of measurement.

Truck classifications are typically based upon the maximum loaded weight of the truck, typically using the gross vehicle weight rating (GVWR) and sometimes also the gross trailer weight rating (GTWR), and can vary among jurisdictions.


It is derived from the tun , the term applied to a cask of the largest capacity. This could contain a volume between 175 and 213 imperial gallon s (210 and 256  US gal ; 800 and 970  l ), which could weigh around 2,000 pounds (910  kg ) and occupy some 60 cubic feet (1.7  m3 ) of space. [1]

Litre non-SI unit of volume

The litre or liter is an SI accepted metric system unit of volume equal to 1 cubic decimetre (dm3), 1,000 cubic centimetres (cm3) or 1/1,000 cubic metre. A cubic decimetre occupies a volume of 10 cm×10 cm×10 cm and is thus equal to one-thousandth of a cubic metre.

Pound (mass) unit of mass in imperial, US customary, and avoirdupois systems of units

The pound or pound-mass is a unit of mass used in the imperial, United States customary and other systems of measurement. Various definitions have been used; the most common today is the international avoirdupois pound, which is legally defined as exactly 0.45359237 kilograms, and which is divided into 16 avoirdupois ounces. The international standard symbol for the avoirdupois pound is lb; an alternative symbol is lbm, #, and or ″̶.

Kilogram SI unit of mass

The kilogram is the base unit of mass in the metric system, formally the International System of Units (SI), having the unit symbol kg. It is a widely used measure in science, engineering, and commerce worldwide, and is often called a kilo. The kilogram is almost exactly the mass of one litre of water.

In the United Kingdom the (Imperial) ton was formerly a unit of Statute measure, defined as 2,240  lb (1,016  kg ) [lower-alpha 1] [2] From 1965 the UK embarked upon a programme of metrication and gradually introduced metric units, including the tonne (metric ton), defined as 1,000 kg (2,205 lb). The UK Weights and Measures Act 1985 explicitly excluded many units and terms from "use for trade", including the ton (and the term "metric ton" for "tonne"). [3]

Imperial units System of units formerly used in the British Empire and still used in the United Kingdom

The system of imperial units or the imperial system is the system of units first defined in the British Weights and Measures Act of 1824, which was later refined and reduced. The Imperial units replaced the Winchester Standards, which were in effect from 1588 to 1825. The system came into official use across the British Empire. By the late 20th century, most nations of the former empire had officially adopted the metric system as their main system of measurement, although some imperial units are still used in the United Kingdom, Canada and other countries formerly part of the British Empire. The imperial system developed from what were first known as English units, as did the related system of United States customary units.

Metrication in the United Kingdom Chronology of metrication and metrication-related events in the United Kingdom

Metrication in the United Kingdom, the process of introducing the metric system of measurement in place of imperial units, has made steady progress since the mid–20th century but today remains equivocal and varies by context. Most of government, industry and commerce use metric units, but imperial units are officially used to specify journey distances, vehicle speeds and the sizes of returnable milk containers, beer and cider glasses. Imperial units are also often used to describe body measurements and vehicle fuel economy. In schools metric units are taught and used as the norm and imperial units that remain in common usage in the UK must also be taught.

Tonne Metric unit of mass

The tonne, commonly referred to as the metric ton in the United States and Canada, is a non-SI metric unit of mass equal to 1,000 kilograms or one megagram. It is equivalent to approximately 2,204.6 pounds, 1.102 short tons (US) or 0.984 long tons (UK). Although not part of the SI, the tonne is accepted for use with SI units and prefixes by the International Committee for Weights and Measures.

In the United States and Canada [4] a ton is defined to be 2,000 pounds (907 kg).

Where confusion is possible, the 2240 lb ton is called "long ton" and the 2000 lb ton "short ton"; the tonne is distinguished by its spelling, but usually pronounced the same as ton, hence the US term "metric ton". In the UK the final "e" of "tonne" can also be pronounced ( /ˈtʌni/ ), [5] or "metric ton" when it is necessary to make the distinction.

Long ton, also known as the imperial ton or displacement ton, is the name for the unit called the "ton" in the avoirdupois system of weights or Imperial system of measurements. It was standardised in the thirteenth century and is used in the United Kingdom and several other British Commonwealth of Nations countries alongside the mass-based metric tonne defined in 1799.

The short ton is a unit of mass equal to 2,000 pounds-mass. The unit is most commonly used in the United States where it is known simply as the ton.

Where precision is required the correct term must be used, but for many purposes this is not necessary: the metric and long tons differ by only 1.6%, and the short ton is within 11% of both. The ton (any definition) is the heaviest unit of weight typically used in colloquial speech.

The term "ton" is also used to refer to a number of units of volume, ranging from 35 to 100 cubic feet (0.99 to 2.83  m3 ) in capacity.

Volume Quantity of three-dimensional space

Volume is the quantity of three-dimensional space enclosed by a closed surface, for example, the space that a substance or shape occupies or contains. Volume is often quantified numerically using the SI derived unit, the cubic metre. The volume of a container is generally understood to be the capacity of the container; i. e., the amount of fluid that the container could hold, rather than the amount of space the container itself displaces. Three dimensional mathematical shapes are also assigned volumes. Volumes of some simple shapes, such as regular, straight-edged, and circular shapes can be easily calculated using arithmetic formulas. Volumes of complicated shapes can be calculated with integral calculus if a formula exists for the shape's boundary. One-dimensional figures and two-dimensional shapes are assigned zero volume in the three-dimensional space.

The cubic foot is an imperial and US customary (non-metric) unit of volume, used in the United States, and partially in Canada, and the United Kingdom. It is defined as the volume of a cube with sides of one foot (0.3048 m) in length. Its volume is 28.3168 liters or about ​135 of a cubic meter.

Cubic metre SI derived unit of volume

The cubic metre or cubic meter is the SI derived unit of volume. Its SI symbol is m3. It is the volume of a cube with edges one metre in length. An alternative name, which allowed a different usage with metric prefixes, was the stère, still sometimes used for dry measure. Another alternative name, no longer widely used, was the kilolitre.

It can also be used as a unit of energy, expressed as an equivalent of coal burnt or TNT detonated.

In refrigeration, a ton is a unit of power, sometimes called a ton of refrigeration . It is the power required to melt or freeze one short ton of ice per day. The refrigeration ton hour is a unit of energy, the energy required to melt or freeze 124 short ton of ice.

Units of mass/weight

There are several similar units of mass or volume called the ton:

Full name(s)Common nameQuantityNotes
long ton, [6] weight ton, gross ton"ton" (UK) [lower-alpha 2] 2,240  lb (1,016.047  kg )Used in countries such as the United Kingdom and Commonwealth of Nations that formerly used, or still use the Imperial system
short ton, [7] net ton"ton" (US)2,000 lb (907.1847 kg)Used in the U.S., and formerly in Canada
tonne [8] "tonne"; [lower-alpha 2] "metric ton"

(mainly UK)

1,000 kg (2,204.623 lb)Defined in the International System of Units.

Used worldwide.

In the UK, Canada, Australia, and other areas that had used the imperial system, the tonne is the form of ton legal in trade.

1.58% less than the long ton.

ton shortweight [lower-alpha 3] 2240 lbUsed in the iron industry in the 17th and 18th centuries.
ton longweight [lower-alpha 3] 2400 lb [lower-alpha 4] Used in the iron industry in the 17th and 18th centuries.
  1. The "pound" used in this article is the avoirdupois pound.
  2. 1 2 In the UK, the words "ton" and "tonne" are usually pronounced the same way, /tʌn/ . As the imperial ton and the (metric) tonne only differ by 2%, ambiguity is not typically a problem; where accuracy is required in speech, "long ton" or exaggerated pronunciation of "tonne" emphasising the "e", /ˈtʌni/ , are used. [5]
  3. 1 2 The longweight and shortweight tons were used as a means of making an allowance for wastage in an industrial process. The workman is provided with a longweight ton and is expected to return a shortweight ton of processed product. These measures were particularly used in the operation of hammering iron blooms into shape. [9]
  4. In other industries, a different longweight ton might be used. Coal miners delivered coal to the surface in longweight tons but were paid only for a shortweight ton. This was supposedly to allow for "dirt" (non-coal rocks) in the output. Mine owners, however, were free to set the value of the longweight ton at a value of their own choosing, and in at least some cases, it was set to 25 cwt (2800 lb) compared to the 20 cwt shortweight ton. This was a source of discontent amongst the miners who saw the practice as unfair in favour of the mine owners. [10]

Other units of mass/weight

Both the long ton and the short ton are 20 hundredweight, the long hundredweight and the short hundredweight being 112 and 100 pounds respectively. Before the twentieth century there were several definitions. Prior to the 15th century in England, the ton was 20 hundredweight, each of 108 lb, giving a ton of 2,160 pounds (980 kg).[ citation needed ] In the nineteenth century in different parts of Britain, definitions of 2240, 2352, and 2400 lb were used, with 2000 lb for explosives; the legal ton was usually[ sic ] 2240 lb. [11]

Assay ton (abbreviation 'AT') is not a unit of measurement but a standard quantity used in assaying ores of precious metals. A short assay ton is 29 16 grams while a long assay ton is 32 23 gram. These amounts bear the same ratio to a milligram as a short or long ton bears to a troy ounce. Therefore, the number of milligrams of a particular metal found in a sample weighing one assay ton gives the number of troy ounces of metal contained in a ton of ore.

In documents that predate 1960 the word ton is sometimes spelled tonne,[ citation needed ] but in more recent documents tonne refers exclusively to the metric ton.

In nuclear power plants tHM and MTHM mean tonnes of heavy metals, and MTU means tonnes of uranium. In the steel industry, the abbreviation THM means 'tons/tonnes hot metal', which refers to the amount of liquid iron or steel that is produced, particularly in the context of blast furnace production or specific consumption.

A dry ton or dry tonne has the same mass value, but the material (sludge, slurries, compost, and similar mixtures in which solid material is soaked with or suspended in water) has been dried to a relatively low, consistent moisture level (dry weight). If the material is in its natural, wet state, it is called a wet ton or wet tonne.


In the Imperial units system, the imperial (long) ton is equivalent to 20 hundredweight, a hundredweight being eight stone, and a stone weighing 14 pounds.

Units of volume

The displacement, essentially the weight, of a ship is traditionally expressed in long tons.[ citation needed ] To simplify measurement it is determined by measuring the volume, rather than weight, of water displaced, and calculating the weight from the volume and density. [12] For practical purposes the displacement ton (DT) is a unit of volume, 35 cubic feet (0.9911 m3), the approximate volume occupied by one ton of seawater (the actual volume varies with salinity and temperature). [13] It is slightly less than the 224 imperial gallons (1.018 m3) of the water ton (based on distilled water).

One measurement ton or freight ton is equal to 40 cubic feet (1.133 m3),[ citation needed ] but historically it has had several different definitions. It is sometimes abbreviated as "MTON".[ citation needed ] It is used to determine the amount of money to be charged as "Freight" in carrying different sorts of cargo.[ citation needed ] In general if a cargo is heavier than salt water, the actual tonnage is used. If it is lighter than salt water, e.g. feathers, freight is calculated using Measurement Tons of 40 cubic feet. [14] [15] [16] [17] The freight ton represents the volume of a truck, train or other freight carrier.[ citation needed ] In the past it has been used for a cargo ship but the register ton is now preferred.[ citation needed ] It is correctly abbreviated as "FT"[ citation needed ] but some users are now using freight ton to represent a weight of 1 tonne (1,000 kg; 2,205 lb),[ citation needed ] thus the more common abbreviations are now M/T, MT, or MTON (for measurement ton),[ citation needed ] which may cause it to be confused with the megatonne.

The register ton is a unit of volume used for the cargo capacity of a ship, defined as 100 cubic feet (2.832 m3).[ citation needed ] It is often abbreviated RT or GRT for gross registered ton.[ citation needed ] (The former providing confusion with the refrigeration ton). It is known as a tonneau de mer in Belgium,[ citation needed ] but, in France, a tonneau de mer is 1.44 cubic metres (50.85 cu ft).[ citation needed ]

The Panama Canal/Universal Measurement System (PC/UMS) is based on net tonnage, modified for Panama Canal billing purposes. PC/UMS is based on a mathematical formula to calculate a vessel's total volume; a PC/UMS net ton is equivalent to 100 cubic feet of capacity. [18]

The water ton is used chiefly in Great Britain, in statistics dealing with petroleum products, and is defined as 224 imperial gallons (35.96 cu ft; 1.018 m3), [19] the volume occupied by 1 long ton (2,240 lb; 1,016 kg) of water under the conditions that define the imperial gallon.

Units of energy and power

Ton of TNT

Note that these are small calories (cal). The large or dietary calorie (Cal) is equal to one kilocalorie (kcal), and is gradually being replaced by the latter correct term.

Early values for the explosive energy released by trinitrotoluene (TNT) ranged from 900 to 1100 calories per gram. In order to standardise the use of the term TNT as a unit of energy, an arbitrary value was assigned based on 1000 calories (1 kcal or 4.184  kJ) per gram. Thus there is no longer a direct connection to the chemical TNT itself. It is now merely a unit of energy that happens to be expressed using words normally associated with mass (e.g., kilogram, tonne, pound). [20] [21] The definition applies for both spellings: ton of TNT and tonne of TNT.

Measurements in tons of TNT have been used primarily to express nuclear weapon yields, though they have also been used since in seismology as well.

Tonne of oil equivalent

A tonne of oil equivalent (toe), sometimes ton of oil equivalent, is a conventional value, based on the amount of energy released by burning one tonne of crude oil. The unit is used, for example, by the International Energy Agency (IEA), for the reported world energy consumption as TPES in millions of toe (Mtoe). [22]

Unit conversion factors for toe
toe MWh GJ Gcal MMBtu tce
Source: conversion factors as used by the IEA [23]

Other sources convert 1 toe into 1.28 tonne of coal equivalent (tce). [24] 1 toe is also standardized as 7.33 barrel of oil equivalent (boe). [25]

Tonne of coal equivalent

A tonne of coal equivalent (tce), sometimes ton of coal equivalent, is a conventional value, based on the amount of energy released by burning one tonne of coal. Plural name is tonnes of coal equivalent.

Unit conversion factors for tce
tce MWh GJ Gcal MMBtu toe
Source: conversion factors as used by the IEA [23]


The unit ton is used in refrigeration and air conditioning to measure the rate of heat absorption. Prior to the introduction of mechanical refrigeration, cooling was accomplished by delivering ice. Installing one ton of mechanical refrigeration capacity replaced the daily delivery of one ton of ice.

A refrigeration ton should be regarded as power produced by a chiller when operating in standard AHRI conditions, which are typically 44 °F (7 °C) for chilled water unit, and 95 °F (35 °C) air entering the condenser. This is commonly referred to as "true ton". Manufacturers can also provide tables for chillers operating at other chilled water temperature conditions (as 65 °F or 18.3 °C) which can show more favorable data, which are not valid when making performance comparisons among units unless conversion rates are applied.[ citation needed ]

The refrigeration ton is commonly abbreviated as RT.

Informal tons

See also

Related Research Articles

United States customary units are a system of measurements commonly used in the United States. The United States customary system developed from English units which were in use in the British Empire before the U.S. became an independent country. However, the United Kingdom's system of measures was overhauled in 1824 to create the imperial system, changing the definitions of some units. Therefore, while many U.S. units are essentially similar to their Imperial counterparts, there are significant differences between the systems.

Metric system Decimal system of units of measurement

The metric system is an internationally recognised decimalised system of measurement. It is in widespread use, and where it is adopted, it is the only or most common system of weights and measures. It is now known as the International System of Units (SI). It is used to measure everyday things such as the mass of a sack of flour, the height of a person, the speed of a car, and the volume of fuel in its tank. It is also used in science, industry and trade.

The quintal or centner is a historical unit of mass in many countries which is usually defined as 100 base units of either pounds or kilograms. It is commonly used for grain prices in wholesale markets in India, where 1 quintal = 100 kg.

Tonnage is a measure of the cargo-carrying capacity of a ship. The term derives from the taxation paid on tuns or casks of wine. In modern maritime usage, "tonnage" specifically refers to a calculation of the volume or cargo volume of a ship. Tonnage should not be confused with displacement, which refers to the actual weight of the vessel. Tonnage is commonly used to assess fees on commercial shipping.

Bushel unit of volume

A bushel is an imperial and US customary unit of volume based upon an earlier measure of dry capacity. The old bushel was equal to 2 kennings (obsolete), 4 pecks or 8 dry gallons and was used mostly for agricultural products such as wheat. In modern usage, the volume is nominal, with bushels denoting a mass defined differently for each commodity.

Hundredweight unit of mass, with differing values

The hundredweight, formerly also known as the centum weight or quintal, is an English, imperial, and US customary unit of weight or mass of various values. Its value differs between the American and imperial systems. The two values are distinguished in American English as the "short" and "long" hundredweight and in British English as the "cental" and the "imperial hundredweight".

Barrel (unit) unit of volume

A barrel is one of several units of volume applied in various contexts; there are dry barrels, fluid barrels, Oil Barrels and so forth. For historical reasons the volumes of some barrel units are roughly double the volumes of others; volumes in common usage range from about 100 to 200 litres. In many connections the term "drum" is used almost interchangeably with "barrel".

A system of measurement is a collection of units of measurement and rules relating them to each other. Systems of measurement have historically been important, regulated and defined for the purposes of science and commerce. Systems of measurement in use include the International System of Units (SI), the modern form of the metric system, the imperial system, and United States customary units.

Specific energy is energy per unit mass. It is used to quantify, for example, stored heat and other thermodynamic properties of substances such as specific internal energy, specific enthalpy, specific Gibbs free energy, and specific Helmholtz free energy. It may also be used for the kinetic energy or potential energy of a body. Specific energy is an intensive property, whereas energy and mass are extensive properties.

History of measurement

The earliest recorded systems of weights and measures originate in the 3rd or 4th millennium BC. Even the very earliest civilizations needed measurement for purposes of agriculture, construction, and trade. Early standard units might only have applied to a single community or small region, with every area developing its own standards for lengths, areas, volumes and masses. Often such systems were closely tied to one field of use, so that volume measures used, for example, for dry grains were unrelated to those for liquids, with neither bearing any particular relationship to units of length used for measuring cloth or land. With development of manufacturing technologies, and the growing importance of trade between communities and ultimately across the Earth, standardized weights and measures became critical. Starting in the 18th century, modernized, simplified and uniform systems of weights and measures were developed, with the fundamental units defined by ever more precise methods in the science of metrology. The discovery and application of electricity was one factor motivating the development of standardized internationally applicable units.

Comparison of the imperial and US customary measurement systems

Both the imperial and United States customary systems of measurement derive from earlier English systems used in the Middle Ages, that were the result of a combination of the local Anglo-Saxon units inherited from German tribes and Roman units brought by William the Conqueror after the Norman Conquest of England in 1066.

Because energy is defined via work, the SI unit for energy is the same as the unit of work – the joule (J), named in honor of James Prescott Joule and his experiments on the mechanical equivalent of heat. In slightly more fundamental terms, 1 joule is equal to 1 newton metre and, in terms of SI base units

Ship measurements consist of a multitude of terms and definitions specifically related to ships and measuring or defining their characteristics.

Introduction to the metric system

The metric system was developed during the French Revolution to replace the various measures previously used in France. The metre is the unit of length in the metric system and was originally based on the dimensions of the earth, as far as it could be measured at the time. The litre, is the unit of volume and was defined as one thousandth of a cubic metre. The metric unit of mass is the kilogram and it was defined as the mass of one litre of water. The metric system was, in the words of French philosopher Marquis de Condorcet, "for all people for all time".

Imperial and US customary measurement systems English (pre 1824), Imperial (post 1824) and US Customary (post 1776) units of measure

The imperial system of measurement and the US customary system of measurement are both derived from an earlier English system of measurement which in turn can be traced back to Ancient Roman units of measurement, and Carolingian and Saxon units of measure.

The sack was an English unit of weight or mass used for coal and wool. It has also been used for other commodities by weight, commodities by volume, and for both weight and volume in the United States.


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