Final answer:
Length is measured from longest to shortest by arranging metric units such as kilometers, meters, and millimeters, with millimeters being the smallest. Kilometers are used for long distances, like city-to-city measurements, and micrometers for very small items like the width of a human hair.
Step-by-step explanation:
Length is the measurement of how far two points are from each other. It is usually measured along the greatest dimension of an object. The SI basic unit of length is the meter (m), which can be used to measure all lengths, although different situations may call for different units.
For example, the width of a room might be expressed as 5 meters, while the distance between two cities like New York and Chicago is better expressed in kilometers (km), and very small distances can be measured in millimeters (mm) or micrometers (μm), such as the diameter of a human hair, which is about 10 to 20 μm.
When arranging the metric units of length from longest to shortest, one would list kilometers, meters, and then millimeters, with a millimeter being the smallest measurement unit indicated on most rulers suited for tiny measurements.