# Metre

## Metre

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 = 106 m
• the gigametre : 1 Gm = 109 m
• the terametre : 1 Tm = 1012 m
• the petametre : 1 Pm = 1015 m
• the exametre : 1 Em = 1018 m
• the zettametre : 1 Zm = 1021 m
• the yottametre : 1 Ym = 1024 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.