The same as instruments to measure lengths in any other system: rulers, tape measures, range finders, and so on.
there are many instruments used to measure length depending upon the size of object , Ruler is Metric instrument used to measure length. Screw gauge is also used as an instrument used to measure length in mm.
metric ruler
meter stick
A ruler is an example of an instrument that can be used to measure relatively small linear distances, though it could not measure all three at once.
The metric unit of length is the 'meter'.
there are many instruments used to measure length . measuring tape is used to measure the length of room.
Metres
metre
measure liquids , measure length,.....
the ruler The meter stick
Kilometer and centimeter
The meter.