For other meanings, see Slug (disambiguation)

The slug is an English and U.S. customary unit of mass. The slug is part of a subset of coherent units known as the gravitaional foot-pound-second system, one of several such specialized systems of mechanical units. It is the mass that accelerates by <math> \left( \frac{\mbox{1 ft}}{\mbox{s}^2} \right)<math> when a force of one pound-force (lbf) is exerted on it. Therefore a slug is about 32.174 05 pounds or 14.593 90 kg.

The term metric slug appears as a footnote in the 1967 seventh editon of Marks Standard Handbook for Mechanical Engineers. Also called a hyl, or the TME from a German acronym, it is the mass that accelerates at 1 m/s² under a force of 1 kgf. Because 1 kgf = 9.806 65 N, the metric slug is 9.806 65 kg.

A more complete discussion of imperial and U.S. customary units of force and mass is given at pound.