length
Length is the measurement of the extent of something along its greatest dimension. The SI basic unit of length, or linear measure, is the meter m . All measurements of length may be made in meters, though the prefixes listed in various tables will often be more convenient. The width of a room may be expressed as about 5 meters m , whereas a large distance, such as the distance between New York City and Chicago, is better expressed as 1150 kilometers km . Very small distances can be expressed in units such as the millimeter or the micrometer. The width of a typical human hair is about 20 micrometers m .