# Definition:Metric System/Length/Metre

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## Metre

The metre is the SI base unit of length.

It is defined as the distance travelled by light in vacuum in $\dfrac 1 {299 \ 792 \ 458}$ of a second.

### Conversion Factors

 $\ds$  $\ds 1$ metre $\ds$ $=$ $\ds 100$ centimetres $\ds$ $=$ $\ds 1000$ millimetres $\ds$ $=$ $\ds 1 \, 000 \, 000$ micrometres $\ds$ $=$ $\ds 39 \cdotp 3708$ inches $\ds$ $=$ $\ds 3 \cdotp 28$ feet $\ds$ $=$ $\ds 1 \cdotp 09$ yards

### Symbol

$\mathrm m$

The symbol for the metre is $\mathrm m$.

Its $\LaTeX$ code is \mathrm m .

## Square Metre

The square metre is the SI unit of area.

The symbol for the square metre is $\mathrm m^2$.

## Cubic Metre

The cubic metre is the SI unit of volume.

The symbol for the cubic metre is $\mathrm m^3$.

## Historical Note

It differs from the modern metre by half a centimetre.

It was soon established that as Acceleration Due to Gravity varies considerably according to location, this was not a sustainable definition to maintain a standard.

• 26 March 1791: this proposal was adopted.
• 1805: Ferdinand Rudolph Hassler brought a standard metre made in Paris to the United States. He designed a baseline apparatus which instead of bringing different bars in actual contact during measurements, used only one bar calibrated on the metre and optical contact. Thus the metre became the unit of length for geodesy in the United States.
• 1889: The international prototype metre was defined as the distance between two lines on a standard bar composed of an alloy of $90 \%$ platinum and $10 \%$ iridium, measured at the melting point of ice.

## Linguistic Note

The word metre originated with Tito Livio Burattini who pioneered the concept of a universal set of fundamental units.

He used the term metro cattolico from the Greek μέτρον καθολικόν (métron katholikón), that is universal measure.

This word gave rise to the French word mètre which was introduced into the English language in $1797$.

The spelling metre is the one adopted by the International Bureau of Weights and Measures.

Meter is the variant used in standard American English, but can be confused for the word for a general device used to measure something, in particular the standard household electricity meter, water meter and so on.

While $\mathsf{Pr} \infty \mathsf{fWiki}$ attempts in general to standardise on American English, the name of this unit is one place where a deliberate decision has been made to use the international spelling.