The basic unit of length in the International System of Units.

### Properties

- One metre is equal to 10 decimetres, 100 centimetres and 1000 millimetres.
- One kilometre is equal to 1000 metres.

### Notations

The multiples of the metre are :

- the decametre : 1 dam = 10 m
- the hectometre : 1 hm = 100 m
- the kilometre : 1 km = 1 000 m
- the megametre : 1 Mm = 10
^{6}m - the gigametre : 1 Gm = 10
^{9}m - the terametre : 1 Tm = 10
^{12}m - the petametre : 1 Pm = 10
^{15}m - the exametre : 1 Em = 10
^{18}m - the zettametre : 1 Zm = 10
^{21}m - the yottametre : 1 Ym = 10
^{24}m

The submultiples of the metre are :

- the decimetre : 1 dm = 0,1 m
- the centimetre : 1 cm = 0,01 m
- the millimetre : 1 mm = 0,001 m
- the micrometre : 1 µm = 10
^{-6}m - the nanometre : 1nm = 10
^{-9}m - the picometre : 1 pm = 10
^{-12}m - the femtometre : 1 fm = 10
^{-15}m - the attometre : 1 am = 10
^{-18}m - the zeptometre : 1 zm = 10
^{-21}m - the yoctometre : 1 ym = 10
^{-24}m

### Educational note

The value of the metre is based on a universal constant, the speed of light in a vacuum. It corresponds to the length of the path travelled by light in a vacuum during a time interval of \(\frac{1}{299\space 792\space 458}\) of a second.

Until 1960, the metre was defined as a length equal to one ten-millionth of the length of a quadrant along the Earth’s meridian.