In chemistry, the path length is defined as the distance that light (UV/VIS) travels through a sample in an analytical cell. Typically, a sample cell is made of quartz, glass, or a plastic rhombic cuvette with a volume typically ranging from 0.1 mL to 10 mL or larger used in a spectrophotometer. For the purposes of spectrophotometry (i.e. when making calculations using the Beer-Lambert law) the path length is measured in centimeters (rather than in meters).

In a computer network, the path length is one of many possible router metrics used by a router to help determine the best route among multiple routes to a destination. It consists of the end-to-end hop count from a source to a destination over the network.

More simply, in general computer terminology, it can mean simply the total number of instructions executed from point A to point B in a program - Instruction path length.

In physics, the path length is defined as the total distance an object travels. Unlike displacement, which is the total distance an object travels from a starting point, path length is the total distance travelled, regardless of where it travelled.