How much of the teaching content at universities in the US is delivered in imperial units instead of SI?

I imagine that industry (e.g. Engineering) is still stuck using imperial units, but research and physics are much better suited to SI units, so I am interested to know how this is dealt with.

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    I think a good part of Europe is still stuck with CGS, too. Commented Mar 27, 2014 at 14:00
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    Very interesting... in Australia anything other than SI units is practically unheard of
    – xyz
    Commented Mar 27, 2014 at 14:24
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    Let me paraphrase real life: if you're a mechanical engineer in the U.S. and have no idea what ft-lb, kips or ksi are, you're in for a world of hurt. Commented Mar 28, 2014 at 0:20
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    It would be malpractice for any university not to teach students to perform dimensional analysis on the inputs to any kind of problem before proceeding.
    – Erik
    Commented Jan 24, 2015 at 16:51
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    it's interesting to note that American units aren't actually imperial units, they are similar but different eg pints and gallons are not the imperial ones.
    – Mark Joshi
    Commented Sep 29, 2015 at 22:50

4 Answers 4


When I was an (engineering, US) undergrad, the textbook in one engineering mechanics class included problems using SI units and problems using imperial units. The problem sets for homework and exams came from the book, and could be in either SI or imperial units.

(You can see these examples in a sample chapter).

Every other class I've taken as a physics and engineering student used SI units exclusively.

  • I had the same experience, except that I recall some textbooks also included a few problems in cgs just to keep us on our toes. But probably 99% of it was SI.
    – mhwombat
    Commented Jan 15, 2015 at 11:51
  • This was my experience, modulo thermodynamics and heat transfer instead of engineering mechanics.
    – aeismail
    Commented Jan 24, 2015 at 15:51

At the US community college where I teach physics, SI is used exclusively in all science courses. (Chem courses do still use calories, which are not SI.) Nearly all physics textbooks use SI exclusively, although a few may mix in examples using feet and pounds here and there.

  • This. When I was an undergrad most of my texts used SI but regularly mentioned both the cgs and imperial equivalents when introducing a new quantity. Now the practice seems to be fading away. I don't entirely approve as some of my students are heading for civil engineering and the old ways persist in that discipline. So I introduce the equivalents in lecture, but I don't test my students on them. Commented Sep 29, 2015 at 23:00

In civil engineering, imperial units are used exclusively. Sometimes instructors will mention SI units, but you will never use them on homework or exams.

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    Really?!? Can you point to examples? I find it hard to believe that this is still being done, since pretty much every other discipline uses SI...
    – jakebeal
    Commented Jan 24, 2015 at 15:41
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    @jakebeal: This would make sense as the engineering codes that govern building in the US are still largely written in "traditional" units.
    – aeismail
    Commented Jan 24, 2015 at 15:55
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    @aeismail Sometimes, I despair of my country.
    – jakebeal
    Commented Jan 24, 2015 at 17:31
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    @aeismail I'm sure that it was a huge effort for the UK and Australia and Canada to change over as well, back in the 70s and 80s, but ends up a lot better than the current polyglot system of partial metric.
    – jakebeal
    Commented Jan 24, 2015 at 20:23
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    US lumber is still its own weird case where length is real inches and thickness is in nominal inches...
    – keshlam
    Commented Sep 29, 2015 at 20:36

First, a remark which I think important (apologies, I'm donning my metrologist's hat). Nowadays, the units of the Imperial system or those of the CGS are all defined in terms of the SI units. For instance, 1 inch equals 2.54 centimetre by definition, and the centimetre in that definition is really the SI centimetre. This means that even in fields where non-SI units are traditionally employed, a basic knowledge of the SI is at least needed if one has to discuss units-related stuff.

I imagine that industry (e.g. Engineering) is still stuck using imperial units

Yes, you can still find pressures measured in pound-force per square inch (psi) or inch of mercury (inHg), areas measured in circular mil, heat measured in British thermal unit (BTU), wrench sizes measured in fractions of inch, etc. Product data sheets sometimes list parameters both in Imperial and SI units, sometimes no.

but research and physics are much better suited to SI units

Yes, Imperial units are definitely ill-suited for science. As for the dichotomy SI/CGS that has been brought up in the comments... uh, well, opinions might differ across disciplines, and if you skim through publications (journals, books) of different disciplines you will find different level of adherence to the SI (e.g. there are recent physics books which use the SI when discussing mechanics and the CGS when discussing electromagnetism).

How much of the teaching content at universities in the US is delivered in imperial units instead of SI?

I cannot answer this question directly because my contacts with the US are within my discipline and mainly outside of academia. However, I can try to answer it in an indirect way from the (limited) perspective of a compulsive book-buyer (that's me), assuming that the teaching content of lectures is roughly the same of books.

If I look at the books in my library, all the engineering books on electronics and electromagnetics written by US authors, even those from the 1960s, employ the SI. I could find only one exception, a book on lens design from the 1970s which employs Imperial units. None of the physics books employ Imperial units. Instead, the few mechanical engineering books that I have employ Imperial units, but they are very old.

Therefore, my impression, as reader of technical and scientific books from the other side of the ocean, is that nowadays most of the teaching content in the US is delivered in SI units, and that Imperial units are really limited to a few fields.

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