The poundal is a non-SI unit of force. It is a part of the absolute foot-pound-second system of units, a coherent subsystem of English units introduced in 1879, and one of several specialized subsystems of mechanical units used as aids in calculations. It is defined as 1 lb·ft·s^-2, or in words, as the force necessary to accelerate a pound of mass at 1 foot per second, per second.

English units require either re-scaling of either force or mass to eliminate a numerical proportionality constant in the equation $F\; =\; ma$. The poundal represents one choice, which is to rescale units of force. Since a pound of force accelerates a pound of mass at about 32 ft/s² (the acceleration of gravity = g), the smaller unit of force represented by the poundal is chosen as that force which accelerates a 1-pound mass at 1 foot per second^2. The poundal is only about 1/32 of a pound of force.

The poundal-force, pound-mass system is contrasted with an alternate system in which pounds are used as force, and instead, the mass unit is rescaled by a factor of 32. If force is given in pounds rather than poundals, then an acceleration of one foot per second^2 is induced in a mass of about 32 pounds mass, for each applied pound of force. The mass unit of about 32 mass-pounds (32.2 to three digits) in this alternate system, is called a slug.

Note that slugs and poundals are never used in the same system, since each exists to solve the same problem, so that both should not be used together.

1 pdl = 0.138 254 954 376 newton (N) exactly

Units of force | Imperial units | Customary units in the United States

Poundal | Poundal | パウンダル