English Engineering Units

Some fields of engineering in the United States use a system of measurement of physical quantities known as the English Engineering Units.[1][2] Despite its name, the system is based on United States customary units of measure; it is not used in England.

A similar system, termed British Engineering Units by Halliday and Resnick (1974), was a system that used the slug as the unit of mass, and in which Newton's law retains the form F = ma.[3] Modern British engineering practice has used SI base units since at least the late 1970s.[4]


The English Engineering Units is a system of consistent units used in the United States. The set is defined by the following units,[5] with a comparison of their definitive conversions to their International System of Units counterparts.[6]

Dimension English Engineering Unit SI unit Exact conversion
timesecond (s)second (s)1 s
lengthfoot (ft)metre (m)0.3048 m
masspound mass (lb)kilogram (kg)0.45359237 kg
forcepound-force (lbf)newton (N)4.4482216152605 N
temperaturedegree Fahrenheit (°F)degree Celsius (°C)59 °C[lower-alpha 1]
absolute temperaturedegree Rankine (°R)kelvin (K)59 K

Units for other physical quantities are derived from this set as needed.

In English Engineering Units, the pound-mass and the pound-force are distinct base units, and Newton's Second Law of Motion takes the form F =  ma/gc, where gc = 32.174 lb·ft/(lbf·s2).

History and etymology

The term English units strictly refers to the system used in England until 1826, when it was replaced by (more rigorously defined) Imperial units. The United States continued to use the older definitions until the Mendenhall Order of 1893, which established the United States customary units. Nevertheless, the term "English units" persisted in common speech and was adapted as "English engineering units" but these are based on US customary units rather than the pre-1826 English system.

See also


  1. Comings, E. W. (1940). "English Engineering Units and Their Dimensions". Ind. Eng. Chem. 32 (7): 984–987. doi:10.1021/ie50367a028.
  2. Klinkenberg, Adrian (1969). "The American Engineering System of Units and Its Dimensional Constant gc". Ind. Eng. Chem. 61 (4): 53–59. doi:10.1021/ie50712a010.
  3. Halliday, David; Resnick, Robert (1974). Fundamentals of Physics (revised printing ed.). New York: Wiley. pp. 35, 68–69.
  4. Railway Construction and Operation Requirements – Structural and Electrical Clearances (PDF). London: Department of Transport. 1977. ISBN 0-11-550443-5. Retrieved 29 March 2012. 1.2 These new sections represent the first stage of a complete revision and metrication of the 'Railway Construction and Operation Requirements for Passenger Lines and Recommendations for Goods Lines of the Minister of Transport', 1950 (Reprinted 1970). They are published separately in advance of the complete revision because of the urgent need for an up-to-date metric guide to the Department's requirements for clearances, both structural and electrical.
  5. R. Zucker, O. Biblarz (2002). Fundamentals of Gas Dynamics. Hoboken, New Jersey: John Wiley & Sons, Inc. ISBN 0-471-05967-6.
  6. United States. National Bureau of Standards (1959). Research Highlights of the National Bureau of Standards. U.S. Department of Commerce, National Bureau of Standards. p. 13. Retrieved 31 July 2019.


  1. A degree Fahrenheit is about half a degree Celsius. To convert a specific temperature from Fahrenheit to Celsius, subtract 32°F then divide by 9 and multiply by 5. For example, consider 50°F: 50 minus 32 = 18. 18/9 =2. 2x5=10. So 50°F = 10°C. But the subtraction of 32 does not apply to (say) a 50°F temperature change, which equates to a 2779°C change.
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