The metre (Commonwealth English[[1]]) or meter (American English [2]]) (symbol: m) is the SI base unit of length. It is defined as the length of the path travelled by light [[3]]in absolute vacuum during a time [[4]]interval of 1/299,792,458 of a second[[5]].

SI prefixes applied to the metreEdit

Adding SI prefixes to metre creates multiples and submultiples; for example kilometre (1000 metres; kilo- = 1000) and millimetre (one thousandth of a metre; milli- = 1 / 1 000).

The metre may be used with SI prefixes as shown.

Multiple Name Symbol Multiple Name Symbol
100 metre m      
101 decametre dam 10–1 decimetre dm
102 hectometre hm 10–2 centimetre cm
103 kilometre km 10–3 millimetre mm
106 megametre Mm 10–6 micrometre µm
109 gigametre Gm 10–9 nanometre nm
1012 terametre Tm 10–12 picometre pm
1015 petametre Pm 10–15 femtometre fm
1018 exametre Em 10–18 attometre am
1021 zettametre Zm 10–21 zeptometre zm
1024 yottametre Ym 10–24 yoctometre ym


1 metre is equivalent to:

  • exactly 1/0.9144 yards[[6]] (approximately 1.0936 yards)
  • exactly 1/0.3048 feet[[7]](approximately 3.2808 feet)
  • exactly 10000/254 inches[[8]] (approximately 39.370 inches)

History Edit

See History at [[9]]

Timeline of definition Edit

  • May 8 1790 — The National Assembly (French Revolution) [[10]]decides that the length of the new metre would be equal to the length of a pendulum with a half-period of one second.
  • March 30 1791 — The French National Assembly accepts the proposal by the French Academy of Sciences [[11]]that the new definition for the metre be equal to one ten-millionth of the length of the earth's meridian (geography)[[12]] along a quadrant (one-fourth the polar circumference of the earth).
  • 1795 — Provisional metre bar constructed of brass[[13]].
  • December 10 1799 — The French National Assembly specifies that the platinum metre bar, constructed on 23 June 1799 and deposited in the National Archives, as the final standard.
  • September 28 1889 — The first Conférence Générale des Poids et Mesures [[14]] defines the length as the distance between two lines on a standard bar of an alloy of platinum with ten percent iridium [[15]], measured at the melting point of ice.
  • October 6 1927 — 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 atmospheric pressure [[16]] 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.
  • October 20 1960 — The eleventh CGPM defines the length to be equal to 1,650,763.73 wavelengths [[17]] in vacuum of the electromagnetic radiation [[18]] corresponding to the transition between the 2p10 and 5d5 quantum levels of the krypton-86 atom.
  • October 21 1983 — The seventeenth CGPM defines the length to be distance travelled by light [[19]] in vacuum during a time interval of 1/299 792 458 of a second [[20]].

See also Edit

External links Edit

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