The metric unit for length is the meter. The majority of measured lengths can be found using meters, but if the object is very small or very large it may be measured in other common metric units that are derived from the meter.
Small objects may be measured in either millimeters or centimeters, while longer lengths may be measured in kilometers. Millimeters are equal to 1/1000th of one meter, centimeters are equal to 1/100th of one meter and kilometers are equal to 1000 meters. All of these units are metric units that are used widely around much of the world.