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.
The English Engineering Units is a system of coherent units used in the United States. The set is defined by the following units,[3] and definitive conversions to the International System of Units.[4]
| Dimension | English Engineering Unit | SI unit | Unit conversion |
|---|---|---|---|
| time | second (s) | second (s) | 1 s |
| length | foot (ft) | metre (m) | 0.3048 m |
| mass | pound mass (lb) | kilogram (kg) | 0.45359237 kg |
| force | pound-force (lbf) | newton (N) | 4.4482216152605 N |
| temperature | degree Fahrenheit (°F) | degree Celsius (°C) | 5/9 °C[a] |
| absolute temperature | degree Rankine (°R) | kelvin (K) | 5/9K |
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 
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.
A similar system, termed British Engineering Units by Halliday and Resnick (1974), is a system that uses the slug as the unit of mass, and in which Newton's law retains the form F = ma.[5] Modern British engineering practice has used SI base units since at least the late 1970s.[6]
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.
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