Slug (mass)

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The slug is a unit of mass associated with Imperial units and United States customary units. It is a mass that accelerates by 1 ft/s2 when a force of one pound-force (Template:Lbf) is exerted on it.

One slug has a mass of Template:Val or Template:Val based on standard gravity, the international foot, and the avoirdupois pound.[1] At the surface of the Earth, an object with a mass of 1 slug exerts a force of approximately Template:Val or Template:Val.[2][3]


The slug is part of a subset of units known as the gravitational FPS system, one of several such specialized systems of mechanical units developed in the late 19th and the 20th century. Geepound was another name for this unit in early literature.[4]

The name "slug" was coined before 1900 by British physicist Arthur Mason Worthington,[5] but it did not see any significant use until decades later. A 1928 textbook says:

No name has yet been given to the unit of mass and, in fact, as we have developed the theory of dynamics no name is necessary. Whenever the mass, m, appears in our formulae, we substitute the ratio of the convenient force-acceleration pair (w/g), and measure the mass in lbs. per ft./sec.2 or in grams per cm./sec.2.


The slug is listed in the "Regulations under the Weights and Measures (National Standards) Act, 1960". This regulation defines the units of weights and measures, both regular and metric, in Australia.

Similar units

The blob is the inch version of the slug (1 blob = 1 lbf·s2/in = 12 slugs)[1] or equivalent to 175.126 kg. This unit is also called slinch (a portmanteau of the words slug and inch).[6][7] Slang terms include slugette,[8] and a snail.[9]

Metric units include the "glug" in the centimetre-gram-second system, and the "mug", "par", or "MTE" in the metre-kilogram-second system.[10]


  1. 1.0 1.1 Shigley, Joseph E. and Mischke, Charles R. Mechanical Engineering Design, Sixth ed, pp. 31–33. McGraw Hill, 2001. ISBN 0-07-365939-8.
  2. Beckwith, Thomas G., Roy D. Marangoni, et al. Mechanical Measurements, Fifth ed, pp. 34-36. Addison-Wesley Publishing, 1993. ISBN 0-201-56947-7.
  3. Shevell, R.S. Fundamentals of Flight, Second ed, p. xix. Prentice-Hall, 1989.
  4. [1].
  5. {{#invoke:citation/CS1|citation |CitationClass=book }}
  6. Slug. DiracDelta Science & Engineering Encyclopedia
  7. Template:Cite web
  8. Celmer, Robert. Notes to Accompany Vibrations II. Version 2.2. 2009.
  9. [2]
  10. {{#invoke:citation/CS1|citation |CitationClass=book }}

External links