In Canada the spelling litre is standard, though both liter and litre are common and accepted. However, the unit is always written US style, mL.

It turns out that in siunitx \litre and \liter are not synonyms. \litre gives l while \liter gives L.

I have used \litre quite a few times throughtout my document, and would like to keep using it as it is more natural for me to type; I kept having to go back and retype it the American way while writing this question. This means I'd rather not just do a find and replace.

Is there an easy way that I could either swap these two macros, or make both do a capital L?

I've tried \AtBeginDocument{\renewcommand\litre{\liter}} but then I get errors about undefined arguments and such, so I thought it best to ask.

  • What about overwriting the default \litre with \DeclareSIUnit{\litre}{L} or \DeclareSIUnit{\litre}{\liter}?
    – Guho
    May 13, 2016 at 5:09

1 Answer 1


The unit macros are defined only locally, so you do not want a global setting of \litre. Rather, use




or of course use your editor to do find and replace. (I'd favour making the two logically equivalent over hard-coding L into both.)

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