Fourth graders have to know which metric unit to use in order to measure things properly. For this worksheet on metric units, 4th graders identify when to measure in centimeters, decimeters, meters and kilometers. This worksheet provides a quick practice of this skill. It is from the Houghton Mifflin math series and is tied to a California State Standard.   In this problem solving worksheet, students solve 6 questions involving metric units of length with millimeters, centimeters,