The basic unit of length according to the SI system is the metre. The ratio of length units in the SI system is 10. The table shows the most commonly used length units.

Symbol	Name	Value in metres
km	kilometre	1000 m
hm	hectometre	100 m
dam	decametre	10 m
m	metre	1 m
dm	decimetre	0,1 m
cm	centimetre	0,01 m
mm	millimetre	0,001 m

A smaller unit can be converted into a larger one by dividing its numerical value by the ratio. A larger unit can be converted into a smaller unit by multiplying its value by the ratio.