As per the metric system, the SI unit of length is a meter. Some other units are kilometer, nanometer, milimeters, centimeter, meters and decimeter. Students can read more about it on Metric Length - Explanation, Conversions, SI Unit, Measures, Problems, and FAQs. This page has explained what the system international unit of metric length is along with the other units so that students can understand the units. Conversion of bigger units to the smaller ones have also been explained here.