# Unit of measurement

The former Weights and Measures office in Seven Sisters, London
Units of measurement, Palazzo della Ragione, Padua

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.[1] Any other quantity of that kind can be expressed as a multiple of the unit of measurement.

For example, a length is a physical quantity. The metre is a unit of length that represents a definite predetermined length. When we say 10 metres (or 10 m), we actually mean 10 times the definite predetermined length called "metre".Measurement is a process of determining how large or small a physical quantity is as compared to a basic reference quantity of the same kind.

The definition, agreement, and practical use of units of measurement have played a crucial role in human endeavour from early ages up to the present. A multitude of systems of units used to be very common. Now there is a global standard, the International System of Units (SI), the modern form of the metric system.

In trade, weights and measures is often a subject of governmental regulation, to ensure fairness and transparency. The International Bureau of Weights and Measures (BIPM) is tasked with ensuring worldwide uniformity of measurements and their traceability to the International System of Units (SI).

Metrology is the science of developing nationally and internationally accepted units of measurement.

In physics and metrology, units are standards for measurement of physical quantities that need clear definitions to be useful. Reproducibility of experimental results is central to the scientific method. A standard system of units facilitates this. Scientific systems of units are a refinement of the concept of weights and measures historically developed for commercial purposes.

Science, medicine, and engineering often use larger and smaller units of measurement than those used in everyday life. The judicious selection of the units of measurement can aid researchers in problem solving (see, for example, dimensional analysis).

In the social sciences, there are no standard units of measurement and the theory and practice of measurement is studied in psychometrics and the theory of conjoint measurement.

## History

A unit of measurement is a standardised quantity of a physical property, used as a factor to express occurring quantities of that property. Units of measurement were among the earliest tools invented by humans. Primitive societies needed rudimentary measures for many tasks: constructing dwellings of an appropriate size and shape, fashioning clothing, or bartering food or raw materials.

The earliest known uniform systems of measurement seem to have all been created sometime in the 4th and 3rd millennia BC among the ancient peoples of Mesopotamia, Egypt and the Indus Valley, and perhaps also Elam in Persia as well.

Weights and measures are mentioned in the Bible (Leviticus 19:35–36). It is a commandment to be honest and have fair measures.

In the Magna Carta of 1215 (The Great Charter) with the seal of King John, put before him by the Barons of England, King John agreed in Clause 35 "There shall be one measure of wine throughout our whole realm, and one measure of ale and one measure of corn—namely, the London quart;—and one width of dyed and russet and hauberk cloths—namely, two ells below the selvage..."

As of the 21st Century, multiple unit systems are used all over the world such as the United States Customary System, the British Customary System, and the International System. However, the United States is the only industrialized country that has not yet completely converted to the Metric System. The systematic effort to develop a universally acceptable system of units dates back to 1790 when the French National Assembly charged the French Academy of Sciences to come up such a unit system. This system was the precursor to the metric system which was quickly developed in France but did not take on universal acceptance until 1875 when The Metric Convention Treaty was signed by 17 nations. After this treaty was signed, a General Conference of Weights and Measures (CGPM) was established. The CGPM produced the current SI system which was adopted in 1954 at the 10th conference of weights and measures. Currently, the United States is a dual-system society which uses both the SI system and the US Customary system.[2]

Other Languages
العربية: وحدات قياس
aragonés: Unidat de mesura
asturianu: Unidá de midida
azərbaycanca: Ölçü vahidləri
беларуская: Адзінка вымярэння
беларуская (тарашкевіца)‎: Адзінкі вымярэньня
български: Системи единици
bosanski: Mjerna jedinica
dansk: Måleenhed
Deutsch: Maßeinheit
Esperanto: Mezurunuo
estremeñu: Midía
فارسی: یکا
français: Unité de mesure
Gaeilge: Aonaid
ગુજરાતી: એકમ
한국어: 측정 단위
hrvatski: Mjerna jedinica
Bahasa Indonesia: Satuan
interlingua: Unitate de mesura
íslenska: Mælieining
Kiswahili: Kizio
latviešu: Mērvienība
Lëtzebuergesch: Moosseenheet
македонски: Единица мерка
മലയാളം: ഏകകം
मराठी: एकक
Bahasa Melayu: Unit ukuran

norsk: Måleenhet
norsk nynorsk: Måleining
oʻzbekcha/ўзбекча: Oʻlchov birligi
ਪੰਜਾਬੀ: ਮਾਪ ਇਕਾਈਆਂ
Plattdüütsch: Maateenheit
Runa Simi: Tupu
Sesotho sa Leboa: Motšo
Simple English: Unit of measurement
slovenčina: Fyzikálna jednotka
slovenščina: Merska enota
српски / srpski: Мјерне јединице
srpskohrvatski / српскохрватски: Mjerne jedinice
svenska: Måttenhet
татарча/tatarça: Үлчәү берәмлекләре
తెలుగు: ప్రమాణం
Türkçe: Ölçü birimi
Tiếng Việt: Đơn vị đo