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Encyclopedia > Metre
1 metre =
SI units
1000 mm 100 cm
US customary / Imperial units
3.281 ft 39.37 in

The metre or meter[1](symbol: m) is the fundamental unit of length in the International System of Units (SI). The metre was originally defined by a prototype object meant to represent 110 000 000 the distance between the poles and the Equator. Today, it is defined as 1299 792 458 of a light-second. Look up meter, metre in Wiktionary, the free dictionary. ... â€œSIâ€ redirects here. ... A millimetre (American spelling: millimeter, symbol mm) is an SI unit of length that is equal to one thousandth of a metre. ... A centimetre (American spelling centimeter, symbol cm) is a unit of length that is equal to one hundredth of a metre, the current SI base unit of length. ... U.S. customary units, also known in the United States as English units[1] (but see English unit) or standard units, are units of measurement that are currently used in the USA, in some cases alongside units from SI (the International System of Units â€” the modern metric system). ... The Imperial units are an irregularly standardized system of units that have been used in the United Kingdom and its former colonies, including the Commonwealth countries. ... A foot (plural: feet or foot;[1] symbol or abbreviation: ft or, sometimes, â€² â€“ a prime) is a unit of length, in a number of different systems, including English units, Imperial units, and United States customary units. ... An inch (plural: inches; symbol or abbreviation: in or, sometimes, â€³ - a double prime) is the name of a unit of length in a number of different systems, including English units, Imperial units, and United States customary units. ... For other uses, see American English (disambiguation). ... The SI system of units defines seven SI base units: physical units defined by an operational definition. ... For other uses of this word, see Length (disambiguation). ... â€œSIâ€ redirects here. ... World map showing the equator in red In tourist areas, the equator is often marked on the sides of roads The equator marked as it crosses IlhÃ©u das Rolas, in SÃ£o TomÃ© and PrÃ­ncipe. ... The speed of light in a vacuum is an important physical constant denoted by the letter c for constant or the Latin word celeritas meaning swiftness.[1] It is the speed of all electromagnetic radiation, including visible light, in a vacuum. ...

Because it is the base unit of length in the SI, all SI units which involve length (such as area or speed) are defined relative to the metre. Additionally, due to the metre being the only SI base unit used to measure a vector (e.g. displacement), all vector units are defined relative to the metre. However, decimal multiples and submultiples of the metre— such as kilometre (1000 metres) and centimetre (0.01 metres)— can be formed by adding SI prefixes to metre (see the table below). The SI system of units defines seven SI base units: physical units defined by an operational definition. ... This article is about the physical quantity. ... This article does not cite any references or sources. ... â€œkmâ€ redirects here. ... A centimetre (American spelling centimeter, symbol cm) is a unit of length that is equal to one hundredth of a metre, the current SI base unit of length. ... An SI prefix (also known as a metric prefix) is a name or associated symbol that precedes a unit of measure (or its symbol) to form a decimal multiple or submultiple. ...

## Etymology

The word metre is from the Greek metron (μέτρον), "a measure" via the French mètre. Its first recorded usage in English meaning this unit of length is from 1797.

## History

### Meridional definition

However, in 1793, France adopted the metre based on provisional results from the expedition as its official unit of length. Although it was later determined that the first prototype metre bar was short by a fifth of a millimetre due to miscalculation of the flattening of the Earth, this length became the standard. So, the circumference of the Earth through the poles is approximately forty million metres. This article is about Earth as a planet. ...

### Prototype metre bar

Historical International Prototype Metre bar, made of an alloy of platinum and iridium, which was the standard from 1889 to 1960.

In the 1870s and in light of modern precision, a series of international conferences were held to devise new metric standards. The Metre Convention (Convention du Mètre) of 1875 mandated the establishment of a permanent International Bureau of Weights and Measures (BIPM: Bureau International des Poids et Mesures) to be located in Sèvres, France. This new organisation would preserve the new prototype metre and kilogram when constructed, distribute national metric prototypes, and maintain comparisons between them and non-metric measurement standards. This organization created a new prototype bar in 1889 at the first General Conference on Weights and Measures (CGPM: Conférence Générale des Poids et Mesures), establishing the International Prototype Metre as the distance between two lines on a standard bar of an alloy of ninety percent platinum and ten percent iridium, measured at 0 degrees Celsius. Template:USgov Template:Nist http://www. ... The Metre Convention (or Convention of the Metre, or Convention du Mètre in French, its original language) of 1875 is an international treaty that established what is now known as the SI system. ... The International Bureau of Weights and Measures is the English name of the Bureau international des poids et mesures (BIPM, often written in English Bureau International des Poids et Mesures), a standards organisation, one of the three organizations established to maintain the International System of Units (SI) under the terms... Road to SÃ¨vres, Jean-Baptiste Camille Corot, 1855-1865. ... â€œKgâ€ redirects here. ... The General Conference on Weights and Measures is the English name of the ConfÃ©rence gÃ©nÃ©rale des poids et mesures (CGPM, never GCWM). ... General Name, Symbol, Number platinum, Pt, 78 Chemical series transition metals Group, Period, Block 10, 6, d Appearance grayish white Standard atomic weight 195. ... This article is about the chemical element. ...

### Standard wavelength of krypton-86 emission

In 1893, the standard metre was first measured with an interferometer by Albert A. Michelson, the inventor of the device and an advocate of using some particular wavelength of light as a standard of distance. By 1925, interferometry was in regular use at the BIPM. However, the International Prototype Metre remained the standard until 1960, when the eleventh CGPM defined the metre in the new SI system as equal to 1,650,763.73 wavelengths of the orange-red emission line in the electromagnetic spectrum of the krypton-86 atom in a vacuum. The original international prototype of the metre is still kept at the BIPM under the conditions specified in 1889. Interferometry is the applied science of combining two or more input points of a particular data type, such as optical measurements, to form a greater picture based on the combination of the two sources. ... His signature. ... For other uses, see Wavelength (disambiguation). ... For other uses, see Light (disambiguation). ... It has been suggested that Optical interferometry be merged into this article or section. ... The General Conference on Weights and Measures is the English name of the ConfÃ©rence gÃ©nÃ©rale des poids et mesures (CGPM, never GCWM). ... Look up si, Si, SI in Wiktionary, the free dictionary. ... For other uses, see Wavelength (disambiguation). ... The orange, the fruit from which the modern name of the orange colour comes. ... For other uses, see Red (disambiguation). ... A spectral line is a dark or bright line in an otherwise uniform and continuous spectrum, resulting from an excess or deficiency of photons in a narrow frequency range, compared with the nearby frequencies. ... Legend Î³ = Gamma rays HX = Hard X-rays SX = Soft X-Rays EUV = Extreme ultraviolet NUV = Near ultraviolet Visible light NIR = Near infrared MIR = Moderate infrared FIR = Far infrared Radio waves EHF = Extremely high frequency (Microwaves) SHF = Super high frequency (Microwaves) UHF = Ultra high frequency VHF = Very high frequency HF = High... For other uses, see Krypton (disambiguation). ... Properties For other meanings of Atom, see Atom (disambiguation). ... Look up Vacuum in Wiktionary, the free dictionary. ...

### Standard wavelength of helium-neon laser light

To further reduce uncertainty, the seventeenth CGPM in 1983 replaced the definition of the metre with its current definition, thus fixing the length of the metre in terms of time and the speed of light: Look up time in Wiktionary, the free dictionary. ... The speed of light in a vacuum is an important physical constant denoted by the letter c for constant or the Latin word celeritas meaning swiftness.[1] It is the speed of all electromagnetic radiation, including visible light, in a vacuum. ...

The metre is the length of the path travelled by light in vacuum during a time interval of 1/299 792 458 of a second.[2]

Note that this definition had the effect of fixing the speed of light in a vacuum at precisely 299 792 458 metres per second. Although the metre is now defined in terms of time-of-flight, actual laboratory realisations of the metre are still delineated by counting the required number of wavelengths of light along the distance. An intended byproduct of the 17th CGPM’s definition was that it enabled scientists to measure the wavelength of their lasers with one-fifth the uncertainty. To further facilitate reproducibility from lab to lab, the 17th CGPM also made the iodine-stabilised helium-neon laser "a recommended radiation" for realising the metre. Today's best determination of the wavelength of the relevant transition in 127I2 used for this purpose is λ = 632 991 212.58 fm with an estimated relative standard uncertainty (U) of 2.1 × 10-11. This uncertainty is currently the limiting factor in laboratory realisations of the metre as it is several orders of magnitude poorer than that of the second (U = 5 × 10-16)[3] Consequently, a practical realisation of the metre is usually delineated (not defined) today in labs as 1 579 800.762 042(33) wavelengths of helium-neon laser light in a vacuum.

### Timeline of definition

• 1791 March 30 — The French National Assembly accepts the proposal by the French Academy of Sciences that the new definition for the metre be equal to one ten-millionth of the length of the Earth's meridian along a quadrant through Paris, that is the distance from the equator to the north pole.
• 1795 — Provisional metre bar constructed of brass.
• 1927 October 6 — The seventh CGPM adjusts the definition of the length to be the distance, at 0 °C, between the axes of the two central lines marked on the prototype bar of platinum-iridium, this bar being subject to one standard atmosphere of pressure and supported on two cylinders of at least one centimetre diameter, symmetrically placed in the same horizontal plane at a distance of 571 millimetres from each other.
• 1983 October 21 — The seventeenth CGPM defines the length as equal to the distance travelled by light in vacuum during a time interval of 1/299 792 458 of a second.

## SI prefixed forms of metre

Orders of
magnitude (length)

in E notation

1 E-24 m
1 E-23 m
1 E-22 m
1 E-21 m
1 E-20 m
1 E-19 m
1 E-18 m
1 E-17 m
1 E-16 m
1 E-15 m
1 E-14 m
1 E-13 m
1 E-12 m
1 E-11 m
1 E-10 m
1 E-9 m
1 E-8 m
1 E-7 m
1 E-6 m
1 E-5 m
1 E-4 m
1 E-3 m
1 E-2 m

1 E0 m
1 E+1 m
1 E+2 m
1 E+3 m
1 E+4 m
1 E+5 m
1 E+6 m
1 E+7 m
1 E+8 m
1 E+9 m
1 E+10 m
1 E+11 m
1 E+12 m
1 E+13 m
1 E+14 m
1 E+15 m
1 E+16 m
1 E+17 m
1 E+18 m
1 E+19 m
1 E+20 m
1 E+21 m
1 E+22 m
1 E+23 m
1 E+24 m
1 E+25 m

/

SI prefixes are often employed to denote decimal multiples and submultiples of the metre, as shown in the table below. An SI prefix (also known as a metric prefix) is a name or associated symbol that precedes a unit of measure (or its symbol) to form a decimal multiple or submultiple. ...

SI multiples for metre (m)
Submultiples Multiples
Value Symbol Name Value Symbol Name
10–1 m dm decimetre 101 m dam decametre
10–2 m cm centimetre 102 m hm hectometre
10–3 m mm millimetre 103 m km kilometre
10–6 m μm micrometre (micron) 106 m Mm megametre
10–9 m nm nanometre 109 m Gm gigametre
10–12 m pm picometre 1012 m Tm terametre
10–15 m fm femtometre (fermi) 1015 m Pm petametre
10–18 m am attometre 1018 m Em exametre
10–21 m zm zeptometre 1021 m Zm zettametre
10–24 m ym yoctometre 1024 m Ym yottametre
Common prefixed units are in bold face.[4]

A decimetre is a measurement of length, measuring 10 centimetres or one-tenth of a metre millimetre << centimetre << decimetre << metre << kilometre ... A decametre (American spelling: decameter) (symbol: dam) is a measurement of distance equal to ten metres. ... A centimetre (American spelling centimeter, symbol cm) is a unit of length that is equal to one hundredth of a metre, the current SI base unit of length. ... A hectometre (American spelling: hectometer, symbol hm) is a somewhat uncommonly used unit of length in the metric system, equal to one hundred metres, the current SI base unit of length. ... A millimetre (American spelling: millimeter, symbol mm) is an SI unit of length that is equal to one thousandth of a metre. ... â€œkmâ€ redirects here. ... A micrometre (American spelling: micrometer, symbol Âµm) is an SI unit of length equal to one millionth of a metre, or about a tenth of the diameter of a droplet of mist or fog. ... A megametre (American spelling: megameter, symbol: Mm) is a unit of length equal to 106 metres (from the Greek words megas = big and metro = count/measure). ... A nanometre (American spelling: nanometer, symbol nm) (Greek: Î½Î¬Î½Î¿Ï‚, nanos, dwarf; Î¼ÎµÏ„ÏÏŽ, metrÏŒ, count) is a unit of length in the metric system, equal to one billionth of a metre (or one millionth of a millimetre), which is the current SI base unit of length. ... One picometre is defined as 1x10-12 metres, in standard units. ...

## Equivalents in other units

Metric unit
expressed in non-SI unit
Non-SI unit
expressed in metric unit
1 metre 10−4 mil                1 mil 104 metres
1 metre 39.37 inches                1 inch 0.0254 metres
1 centimetre 0.3937 inch   1 inch 2.54 centimetres
1 millimetre 0.03937 inch   1 inch 25.4 millimetres
1 metre 1×1010 Ångström   1 Ångström 1×10-10 metre
1 nanometre 10 Ångström   1 Ångström 100 picometres

A mil (Norwegian and Swedish for mile) is a unit of length, usually used to measure geographic distance, fairly common in Norway and Sweden. ... A mil (Norwegian and Swedish for mile) is a unit of length, usually used to measure geographic distance, fairly common in Norway and Sweden. ... An inch (plural: inches; symbol or abbreviation: in or, sometimes, â€³ - a double prime) is the name of a unit of length in a number of different systems, including English units, Imperial units, and United States customary units. ... An inch (plural: inches; symbol or abbreviation: in or, sometimes, â€³ - a double prime) is the name of a unit of length in a number of different systems, including English units, Imperial units, and United States customary units. ... A millimetre (American spelling: millimeter, symbol mm) is an SI unit of length that is equal to one thousandth of a metre. ... Scientific notation, also known as standard form, is a notation for writing numbers that is often used by scientists and mathematicians to make it easier to write large and small numbers. ... An Ã¥ngstrÃ¶m or aangstroem (the official transliteration), or angstrom (symbol Ã…) is a non-SI unit of length that is internationally recognized, equal to 0. ... You have big harry skanky balls ...

Look up si, Si, SI in Wiktionary, the free dictionary. ... The Convention du MÃ¨tre of May 20, 1875 is an international treaty that established what is now known as the SI system of units. ... An SI prefix (also known as a metric prefix) is a name or associated symbol that precedes a unit of measure (or its symbol) to form a decimal multiple or submultiple. ... Conversion of units refers to conversion factors between different units of measurement for the same quantity. ... Categories: | ... The speed of light in a vacuum is an important physical constant denoted by the letter c for constant or the Latin word celeritas meaning swiftness.[1] It is the speed of all electromagnetic radiation, including visible light, in a vacuum. ... Metrication or metrification refers to the introduction of the SI metric system as the international standard for physical measurementsâ€”a long-term series of independent and systematic conversions from the various separate local systems of weights and measures. ...

## Notes

1. ^ See American and British English spelling differences
2. ^ Resolution 1 of the seventeenth CGPM (1983): Definition of the metre
3. ^ NIST-F1 Cesium Fountain Atomic Clock.
4. ^ Based upon cutoff point of one million combined Google hits on the plural form of both the international and U.S. spellings. The bolded values returned an aggregate of between 3.66 and 51.4 million hits. Whereas the micrometer is also a device for measuring small distances, a search in September 2007 yielded over four million hits on the two variations of the micrometre. In comparison, the most common prefixed form of the metre that didn’t reach the cutoff threshold—the decimetre—yielded a total of only 322,000 hits even though it is often employed to explain the volume of a litre.

Spelling differences redirects here. ... The litre or liter (see spelling differences) is a unit of volume. ...

## References

Year 2006 (MMVI) was a common year starting on Sunday of the Gregorian calendar. ... is the 154th day of the year (155th in leap years) in the Gregorian calendar. ... Year 2006 (MMVI) was a common year starting on Sunday of the Gregorian calendar. ... is the 154th day of the year (155th in leap years) in the Gregorian calendar. ... Year 2005 (MMV) was a common year starting on Saturday (link displays full calendar) of the Gregorian calendar. ... is the 363rd day of the year (364th in leap years) in the Gregorian calendar. ... Year 2006 (MMVI) was a common year starting on Sunday of the Gregorian calendar. ... is the 154th day of the year (155th in leap years) in the Gregorian calendar. ... Year 2006 (MMVI) was a common year starting on Sunday of the Gregorian calendar. ... is the 154th day of the year (155th in leap years) in the Gregorian calendar. ... Year 2006 (MMVI) was a common year starting on Sunday of the Gregorian calendar. ... is the 154th day of the year (155th in leap years) in the Gregorian calendar. ... Year 2006 (MMVI) was a common year starting on Sunday of the Gregorian calendar. ... is the 154th day of the year (155th in leap years) in the Gregorian calendar. ...

Results from FactBites:

 Online Conversion - The meter (844 words) Although it was later determined that the first prototype metre bar was short by a fifth of a millimetre due to miscalculation of the flattening of the earth, this length became the standard. In 1893, the standard metre was first measured with an interferometer by Albert A. Michelson, the inventor of the device and an advocate of using some particular wavelength of light as a standard of distance. However, the International Prototype Metre remained the standard until 1960, when the eleventh CGPM defined the metre in the new SI system as equal to 1,650,763.73 wavelengths of the orange-red emission line in the electromagnetic spectrum of the krypton-86 atom in a vacuum.
 BIPM - definition of the metre (770 words) The Michelson interferometer was used at the BIPM (by Michelson and Benoît) to determine the length of the metre in terms of the wavelength of the red line of cadmium. The CGPM adopted a definition of the metre in terms of the wavelength in vacuum of the radiation corresponding to a transition between specified energy levels of the The CGPM redefined the metre as the length of the path travelled by light in vacuum during a specific fraction of a second.
More results at FactBites »

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