Millimeter – mm
If we divide a length of 1 meter into 1,000 equal large parts, then every part is a millimeter. The prefix milli means thousandth.
1 millimeter: 1 mm = 1 thousandth meter
100 cm = 10 dm = 1 m = 1,000 mm
Kilometer  km
The prefic kilo means thousand.
1 kilometer: 1 km = thousand meter = 1,000 m
The distance along our roads is often given in whole kilometers. To the right you can see a sign for bicycles where the distance is given in kilometers with decimals.

Foto: Fredrik Enander 

Meter and prefix
By combining a prefix and the unit 1 meter, we can express larger and short lengths than one meter.
Example:
2 Gm = 2 Gigameter = 2,000,000,000 m
64 Nm = 64 Nanometer = 0.000 000 064 m
Swedish Mile (Mil)
1 mile = 10 km = 10,000 m
(Translation note: This is normally a geographic unit used in both Sweden and Norway and is not to be confused with the English or Imperial unit mile. These two are totally separate units.)
A common unit used to indicate longer distances like for example between citys and towns.
An example is the distance between Stockholm and Gothenburg (Göteborg) which is 48 Swedish miles.

Nautical Mile – Sea Mile  minute of arc
Every expression concerning distance and length of 1,852 km.
Nautical traffic uses this unit for length. If you have travelled a nautical mile in an hour, then you have travelled with an average speed of 1 knot.
Astronomical Distances
The Speed of Light
In astronomy, we describe distances with the help of the speed of light. In one second, light travels 7.5 time around the Earth. The distance between the Earth and Sun is 1.496 · 10^{8} km which means that it takes 8 minutes and 14 seconds to travel from the Sun to the Eatch.
LightSecond
The distance light travels in 1 second, in other words, 299,792,458 m.
LightMinute
The distance light travels in 1 minute, in other words, 17,987,547,480 m.
LightHour
The distance light travels in an hour, in other words, 1,079,252,848,800 m.
LightYear
The distance light travels in year, in other words, 9,460,730,472,580,800 m.
The nearest star (besides our own Sun), Alfa Centauri, is about 4.3 lightyears away.
Astronomical Unit  AU
1 AU =149.59787 · 10^{9} m or circa 150 Gm.
1 light year = 63,240 au = 9.4605 · 10^{15} m.
Parsec  pc
30.8568 · 10^{15} m
1 pc = 206,264.8 au = 3.26 lightyears
English measurements
In Great Britain, they enjoy older customs and practices. Because of this, the English have kept their old measurement system while the rest of Europe converted to the Metric System.
