Typically, you will use Meters.
You can measure them with Meter-sticks.
Length is measured in meters in the metric system.
There is only one metric system. Centimetre.
Centimeters
the base unit of length is the metre.
In the English system, probably inches. In the metric system, probably centimetres.
a millimeter
Millimetres
Centimetre
the metric system
Metres
Metres.
Micron