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Is the term "English units" still in current everyday use? I do hear this term among other engineers I work with but I'm unsure if this is a localized usage or is consistent with the wider community.

Mainly I'm focused in the HVAC field but I don't know if terminology would be different in other areas. I noticed that ASHRAE uses the term "IP" or "inch-pound" to refer to what could also be called "English" units, e.g.:

"The ASHRAE Handbook ... is available in I-P (Inch-Pound) or SI (System International) units of measurement."

Formerly I had thought "US customary" was the appropriate term to use.

There might be some subtle technical differences among how "English", "IP", "US customary", or any other scheme is defined. But what I'm interested in is understanding which term mechanical engineers are likely to use in everyday discussion or writing where those technical differences are generally not relevant.

I don't have the impression these units are widely used outside the USA, but I do have an international "audience" in mind so international differences would be interesting, if any.

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    $\begingroup$ US Customary units is the correct name. They have not been legally acceptable units for any commercial purpose in the UK for many years now. I guess a US organization like ASHRAE prefers to call them "English" to hide the fact that only one country in the world still uses them - and it's not England.. $\endgroup$
    – alephzero
    Commented Jun 14, 2019 at 15:13
  • $\begingroup$ @alephzero ASHRAE is calling them "Inch-Pound", not "English" $\endgroup$ Commented Jun 14, 2019 at 15:41
  • $\begingroup$ The main differences between the US & British units is the size of some volumetric quantities: fluid ounce, pint, quart & gallon. Regarding the inch, this was standardized to be 25.4 mm in the 19th century, by convention. The US uses the standardized inch for most applications. For land surveying purposes it still uses the pre standardized inch. $\endgroup$
    – Fred
    Commented Mar 18, 2022 at 12:29
  • $\begingroup$ @alephzero Liberia and Myanmar, too ;) $\endgroup$
    – Phil Sweet
    Commented Mar 18, 2022 at 23:54

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The term "English Units" might be confusing, especially with the English and American...

I believe the term is "Imperial Units" for those in the UK, but not sure how other countries refer to them.

Gallons are defined as US or Imperial and have different volumes. But a gallon does have different volumes in history anyway...

Inch-pounds is a "standard" name, as well as foot-pounds, both used on torque wrenches smaller and larger.

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    $\begingroup$ The term in the UK is "obsolete units." There are UK-born people who are now in their 30s and 40s who don't even know how big they are, because they were never taught them at school and never use them (except for a very few exceptions like miles for road distances and pints for beer) $\endgroup$
    – alephzero
    Commented Jun 14, 2019 at 15:18
  • $\begingroup$ @alephzero yes, and some of the current generation don't even know the current units... $\endgroup$
    – Solar Mike
    Commented Jun 14, 2019 at 15:19
  • $\begingroup$ You are correct that the term in the UK is "Imperial Units". However these have limited statutory acceptance, and this is unlikely to be changed by the UK leaving the EU. $\endgroup$ Commented Dec 21, 2020 at 19:03
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"Imperial" units are not actually, or at least not consistently, the same as the system of units used in the United States. As noted by others in this discussion, the volume of a US Gallon differs, and I seem to recall there are some other differences (though I don't have any specifics to offer here). In any case, because the term "Imperial" is a decidedly poor fit (about as poor as "English"), my preference as a designer of software used by HVAC engineers is the ASHRAE term "Inch-Pound units" which is also expressed as "IP Units". The latter is most commonly used by HVAC engineers in the U.S., as ASHRAE standards for everything from equipment performance tests to energy code requirements and green building performance are widely used throughout the U.S. (and also in many other parts of the world). In other words, because most U.S. HVAC engineers are familiar with and often refer to ASHRAE standards, guidelines, and other technical reference materials, they commonly use the term "IP units".

While I am American and reside in the U.S. state of Oregon, I work for a Scottish company designing software for HVAC engineers both in the U.S. and around the world. And thus I'm all too familiar with the tendency of British engineers to incorrectly re-phrase the term "IP units" as "Imperial units". While this is nearly correct, it is not actually correct. "IP units" is most definitely a contraction of the term "Inch-Pound units", not imperial. It would make me really happy if I could get all of my coworkers in the UK to actually use the term "Inch-Pound units" in a software interface, as using the term "Imperial units" within the interface of a tool used by engineers in the U.S. suggests that those writing the software don't fully understand their audience. While that may seem trivial, knowing how to speak the language of your target audience or product users does make a difference in how they feel about your ability to serve their needs effectively.

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I teach the American Engineering system.

https://www.learnthermo.com/T1-tutorial/ch01/lesson-B/pg04.php

I see references also to it being called the English Engineering system.

https://en.wikipedia.org/wiki/English_Engineering_units

At one point, I remember being taught the inch-pound and ft-slug systems. I imagine the former could still be common in systems where pressure is expressed in pounds per square inch (psia or psig). An analogy is the use of the cgs (centimeter gram second) system by chemical physicists to avoid large exponential factors that would arise otherwise with the mks (meter kilogram second) system

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English units of measure are no longer used in England. Understanding the history of American independence and British colonial rule will clarify their origin.

Prior to American independence the imperial units were used. After independence the use of American imperial units changed according to American standards independent of British imperial units. This explains why US gains are not the same as British gallons.

When UK adopted ISO standards officially, all English measures in engineering became metric standard however, US Imperial measures still remained in use on American soil while rest of the world uses metric based measures.

This is why US imperial units are called English units when in fact they are actually American.

This explanation was given to me by my Civil Engineering head of department at University of Wolverhampton, England where I am a student of civil engineering.

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