Foot–pound–second system of units

The foot–pound–second system is a coherent system of units built on the foot, pound, and second as its base units. It has been used in engineering and mechanics, with distinct versions depending on how the pound is defined.

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Foot (unit): A unit of length equal to 12 inches or exactly 0.3048 metres. It supplies the system’s unit of length.
Coherent system of units: A system in which derived units follow from base units without numerical conversion factors. The FPS name describes a coherent structure, not just three familiar unit names.
British Imperial units: A system of units established in Britain in 1824 and used across the British Empire. FPS grew from British customary and imperial measures rather than a single modern standard.
Engineering mechanics: The application of mechanics principles to analyze forces, motion, and structures in engineered systems. FPS has historically served calculations of forces, motion, and loads.
Pound (unit of mass): A unit of mass equal to 0.45359237 kilograms in the avoirdupois system. In the absolute FPS version, it is the base unit of mass.
Force: An interaction that changes an object's momentum, measured in newtons in SI. The distinction between force and mass separates absolute from engineering FPS.
United States customary units: The customary measurement system used in the United States, derived from earlier British units. Its foot and pound conventions helped sustain engineering uses of FPS.
Structural engineering: The field concerned with designing structures to withstand loads and environmental forces. Building loads and material strengths have often been expressed in FPS units.
Second: The SI base unit of time, defined by a specified transition frequency of caesium-133. It supplies the system’s unit of time.
Poundal: The force that accelerates one pound of mass by one foot per second squared. It is the coherent force unit when the pound is the mass unit.