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 modern use include the
metric system, the imperial system, and
United States customary units.
1.1 Current practice
2 Metric system
3 Imperial and US customary units
4 Natural units
5 Non-standard units
6 Units of currency
7 Historical systems of measurement
7.4 North America
7.6 South America
8 See also
8.1 Conversion tables
9 Notes and references
11 External links
Main article: History of measurement
French Revolution gave rise to the metric system, and this has
spread around the world, replacing most customary units of measure. In
most systems, length (distance), mass, and time are base quantities.
Later science developments showed that either electric charge or
electric current could be added to extend the set of base quantities
by which many other metrological units could be easily defined.
(However, electrical units are not necessary for such a set. Gaussian
units, for example, have only length, mass, and time as base
quantities, and the ampere is defined in terms of other units.) Other
quantities, such as power and speed, are derived from the base set:
for example, speed is distance per unit time. Historically a wide
range of units was used for the same type of quantity: in different
contexts, length was measured in inches, feet, yards, fathoms, rods,
chains, furlongs, miles, nautical miles, stadia, leagues, with
conversion factors which were not powers of ten. Such arrangements
were satisfactory in their own contexts.
The preference for a more universal and consistent system (based on
more rational base units) only gradually spread with the growth of
science. Changing a measurement system has substantial financial and
cultural costs which must be offset against the advantages to be
obtained from using a more rational system. However pressure built up,
including from scientists and engineers for conversion to a more
rational, and also internationally consistent, basis of measurement.
In antiquity, systems of measurement were defined locally: the
different units might be defined independently according to the length
of a king's thumb or the size of his foot, the length of stride, the
length of arm, or maybe the weight of water in a keg of specific size,
perhaps itself defined in hands and knuckles. The unifying
characteristic is that there was some definition based on some
standard. Eventually cubits and strides gave way to "customary units"
to meet the needs of merchants and scientists.
In the metric system and other recent systems, a single basic unit is
used for each base quantity. Often secondary units (multiples and
submultiples) are derived from the basic units by multiplying by
powers of ten, i.e. by simply moving the decimal point. Thus the basic
metric unit of length is the metre; a distance of 1.234 m is
1,234 millimetres, or 0.001234 kilometres.
Main article: Metrication
Metrication is complete or nearly complete in almost all countries. US
customary units are heavily used in the
United States and to some
degree in Liberia. Traditional
Burmese units of measurement are used
in Burma. U.S. units are used in limited contexts in Canada due to the
large volume of trade; there is also considerable use of Imperial
weights and measures, despite de jure Canadian conversion to metric.
A number of other jurisdictions have laws mandating or permitting
other systems of measurement in some or all contexts, such as the
United Kingdom – whose road signage legislation, for instance, only
allows distance signs displaying imperial units (miles or yards)
– or Hong Kong.
In the United States, metric units are used almost universally in
science, widely in the military, and partially in industry, but
customary units predominate in household use. At retail stores, the
liter is a commonly used unit for volume, especially on bottles of
beverages, and milligrams, rather than grains, are used for
medications. Some other standard non-SI units are still in
international use, such as nautical miles and knots in aviation and
Metric system and International
System of Units
A baby bottle that measures in three measurement systems—metric,
imperial (UK), and US customary.
Metric systems of units have evolved since the adoption of the first
well-defined system in France in 1795. During this evolution the use
of these systems has spread throughout the world, first to
non-English-speaking countries, and then to English speaking
Multiples and submultiples of metric units are related by powers of
ten and their names are formed with prefixes. This relationship is
compatible with the decimal system of numbers and it contributes
greatly to the convenience of metric units.
In the early metric system there were two base units, the metre for
length and the gram for mass. The other units of length and mass, and
all units of area, volume, and derived units such as density were
derived from these two base units.
Mesures usuelles (French for customary measurements) were a system of
measurement introduced as a compromise between the metric system and
traditional measurements. It was used in France from 1812 to 1839.
A number of variations on the metric system have been in use. These
include gravitational systems, the centimetre–gram–second systems
(cgs) useful in science, the metre–tonne–second system (mts) once
used in the USSR and the metre–kilogram–second system (mks).
The current international standard metric system is the International
System of Units (Système international d'unités or SI) It is an mks
system based on the metre, kilogram and second as well as the kelvin,
ampere, candela, and mole.
The SI includes two classes of units which are defined and agreed
internationally. The first of these classes includes the seven SI base
units for length, mass, time, temperature, electric current, luminous
intensity and amount of substance. The second class consists of the SI
derived units. These derived units are defined in terms of the seven
base units. All other quantities (e.g. work, force, power) are
expressed in terms of SI derived units.
Imperial and US customary units
Main articles: Imperial and US customary measurement systems, Imperial
units, and US customary units
Both imperial units and
US customary units
US customary units derive from earlier English
Imperial units were mostly used in the former British Empire
and the British Commonwealth, but in all these countries they have
been largely supplanted by the metric system. They are still used for
some applications in the United Kingdom but have been mostly replaced
by the metric system in commercial, scientific, and industrial
applications. US customary units, however, are still the main system
of measurement in the United States. While some steps towards
metrication have been made (mainly in the late 1960s and early 1970s),
the customary units have a strong hold due to the vast industrial
infrastructure and commercial development.
While imperial and US customary systems are closely related, there are
a number of differences between them. Units of length and area (the
inch, foot, yard, mile etc.) are identical except for surveying
purposes.[clarification needed] The
Avoirdupois units of mass and
weight differ for units larger than a pound (lb). The imperial system
uses a stone of 14 lb, a long hundredweight of 112 lb and a
long ton of 2240 lb. The stone is not used in the US and the
hundredweights and tons are short: 100 lb and 2000 lb
Where these systems most notably differ is in their units of volume. A
US fluid ounce (fl oz), about 29.6 millilitres (ml), is slightly
larger than the imperial fluid ounce (about 28.4 ml). However, as
there are 16 US fl oz to a US pint and
20 imp fl oz per imperial pint, the imperial pint is
about 20% larger. The same is true of quarts, gallons, etc. Six US
gallons are a little less than five imperial gallons.
Avoirdupois system served as the general system of mass and
weight. In addition to this there are the Troy and the Apothecaries'
Troy weight was customarily used for precious metals, black
powder and gemstones. The troy ounce is the only unit of the system in
current use; it is used for precious metals. Although the troy ounce
is larger than its
Avoirdupois equivalent, the pound is smaller. The
obsolete troy pound was divided into 12 ounces, rather than the 16
ounces per pound of the
Avoirdupois system. The Apothecaries' system
was traditionally used in pharmacology, but has now been replaced by
the metric system; it shared the same pound and ounce as the troy
system but with different further subdivisions.
Natural units are physical units of measurement defined in terms of
universal physical constants in such a manner that selected physical
constants take on the numerical value of one when expressed in terms
of those units.
Natural units are so named because their definition
relies on only properties of nature and not on any human construct.
Various systems of natural units are possible.
Some other examples are as follows:
Geometric unit systems are useful in relativistic physics. In these
systems the base physical units are chosen so that the speed of light
and the gravitational constant are set equal to unity.
Planck units are a form of geometric units obtained by also setting
Boltzmann's constant, the
Coulomb force constant and the reduced
Planck constant to unity. They are based only on properties of free
space rather than any object or particle.
Stoney units are similar to
Planck units but set the elementary charge
to unity and allow Planck's constant to float (i.e. it is a number
that has to be determined by experiment).
"Schrödinger" units are also similar to
Planck units and also set the
elementary charge to unity, but allow the speed of light to float.
Atomic units are a system of units used in atomic physics,
particularly for describing the properties of electrons. The atomic
units have been chosen such that several the constants relating to the
electron are all equal to one. They are similar to "Schrödinger"
units but set the electron mass to unity and allow the gravitational
constant to float. The unit of energy in this system is the total
energy of the electron in the
Bohr atom and called the Hartree energy.
The unit of length is the Bohr radius.
Electronic units are similar to
Stoney units but set the electron mass
to unity and allow the gravitational constant to float. They are also
similar to atomic units but set the speed of light to unity and allow
Planck's constant to float.
Quantum electrodynamical units are similar to the electronic system of
units except that the proton mass is normalised rather than the
Non-standard measurement units, sometimes found in books, newspapers
The American football field, which has a playing area 100 yards
(91.4 m) long by 160 feet (48.8 m) wide. This is often used
by the American public media for the sizes of large buildings or
parks. It is used both as a unit of length (100 yd or
91.4 m, the length of the playing field excluding goal areas) and
as a unit of area (57,600 sq ft or 5,350 m2), about
1.32 acres (0.53 ha).
British media also frequently uses the football pitch for equivalent
purposes, although soccer pitches are not of a fixed size, but instead
can vary within defined limits (100–130 yd or
91.4–118.9 m long, and 50–100 yd or 45.7–91.4 m
wide, giving an area of 5,000 to 13,000 sq yd or 4,181 to
10,870 m2). However the
UEFA Champions League
UEFA Champions League field must be
exactly 105 by 68 m (114.83 by 74.37 yd) giving an area of
7,140 m2 (0.714 ha) or 8,539 sq yd (1.764 acres).
Example: HSS vessels are aluminium catamarans about the size of a
football pitch... - Belfast Telegraph 23 June 2007
Larger areas are sometimes expressed as a multiple of the areas of
certain American states, or subdivisions of the UK etc.
A ton of TNT equivalent, and its multiples the kiloton, the megaton,
and the gigaton. Often used in stating the power of very energetic
events such as explosions and volcanic events and earthquakes and
asteroid impacts. A gram of TNT as a unit of energy has been defined
as 1000 thermochemical calories (1,000 cal or 4,184 J).
The atom bomb dropped on Hiroshima. Its force is often used in the
public media and popular books as a unit of energy. (Its yield was
roughly 13 kilotons, or 60 TJ.)
One stick of dynamite
Units of currency
A unit of measurement that applies to money is called a unit of
account in economics and unit of measure in accounting. This is
normally a currency issued by a country or a fraction thereof; for
instance, the US dollar and US cent (1⁄100 of a dollar), or the
euro and euro cent.
ISO 4217 is the international standard describing three letter codes
(also known as the currency code) to define the names of currencies
established by the International Organization for Standardization
Historical systems of measurement
Main article: History of measurement
Throughout history, many official systems of measurement have been
used. While no longer in official use, some of these customary systems
are occasionally used in day-to-day life, for instance in cooking.
History of measurement
History of measurement systems in India
Hebrew (Biblical and Talmudic)
French (to 1795)
History of the metric system
Medieval weights and measures
Unit of account
Units of measurement
Weights and measures
Level of measurement
Conversion of units
Notes and references
^ "Statutory Instrument 2002 No. 3113 The Traffic Signs Regulations
and General Directions 2002". Her Majesty's Stationery Office (HMSO).
2002. Retrieved 18 March 2010.
^ HK Weights and Measures Ordinance
^ Financial Accounting Standards Research Initiative: The Unit of
^ M. Ismail Marcinkowski, Measures and Weights in the Islamic World.
An English Translation of Professor Walther Hinz's Handbook
"Islamische Maße und Gewichte", with a foreword by Professor
Bosworth, F.B.A. Kuala Lumpur, ISTAC, 2002, ISBN 983-9379-27-5.
This work is an annotated translation of a work in German by the late
German orientalist Walther Hinz, published in the Handbuch der
Orientalistik, erste Abteilung, Ergänzungsband I, Heft 1, Leiden, The
Netherlands: E. J. Brill, 1970.
Tavernor, Robert (2007), Smoot's Ear: The Measure of Humanity,
CLDR - Unicode localization of currency, date, time, numbers
A Dictionary of Units of Measurement
Old units of measure
Measures from Antiquity and the
Bible Antiquity and the
Bible at the
Wayback Machine (archived May 10, 2008)
Reasonover's Land Measures A Reference to Spanish and French land
measures (and their English equivalents with conversion tables) used
in North America
The Unified Code for Units of Measure
Earth system science
Russell L. Ackoff
William Ross Ashby
Béla H. Bánáthy
Anthony Stafford Beer
Richard E. Bellman
Ludwig von Bertalanffy
Kenneth E. Boulding
C. West Churchman
Edsger W. Dijkstra
Heinz von Foerster
Jay Wright Forrester
Charles A S Hall
James J. Kay
Faina M. Kirillova
Edward Norton Lorenz
Mihajlo D. Mesarovic
James Grier Miller
Howard T. Odum
Manuela M. Veloso
Systems theory in anthropology
Systems theory in archaeology
Systems theory in political science
Systems of measurement
International System of Units
International System of Units (SI)
UK imperial system
US customary units
French (Trad. • Mesures usuelles)
Biblical and Talmudic
Humorous (FFF system)
International System of Units
International System of Units (BIPM)
with special names
Other accepted units
degree of arc
minute of arc
second of arc
Conversion of units
Systems of measurement