To avoid writing down all the units and the associated powers, I wanted to start to use the siunitx package but I have a problem. In fact :

  • The pressure is \SI{10}{\mega\pascal} = "The pressure is 10 MPa"
  • The pressure is 10 \mega\pascal = "The pressure is 10"

In other words, I can't write the units without using \SI{expression}{units}, which is quite restrictive. Does someone have any idea to fix it ?

Thanks in advance.

  • 4
    Welcome to TeX.SX! That's by design: siunitx's units only work inside siunitx's commands. \SI{10}{\mega\pascal} is the correct syntax and you should use that Apr 19, 2021 at 21:08
  • 4
    You can use units with \si {\mega\pascal}, or, simpler, \si{\MPa}, but to be sure to have the correct spacing between number and unit, it's better to use \SI{10}{\MPa}.
    – Bernard
    Apr 19, 2021 at 21:18

3 Answers 3


You can load the package with option free-standing-units, then define


to allow \megapascal in document scope. You might also want unit-optional-argument to allow \megapascal[10], or space-before-unit to allow 10\megapascal to work.

I recommend the standard interface in which units are an argument to \SI.

  • I'm assuming the unit-optional-argument method would produce the space in 10 000 and make a box with the number and unit together (?), for example, where 10\megapascal would not? Apr 20, 2021 at 22:02
  • @likethevegetable Yes
    – Joseph Wright
    Apr 20, 2021 at 22:24

I think I found the answer:



I don't know why it works, but it works! I took all the packages of a friend that could do it and removed it one after the other to figure out that the \sisetup command allows me to do what I wanted.

  • The \sisetupcommand you used here contains options that were only available in version 1 of the siunitx package. If you use this with a more recentversion, you will get a corresponding warning message, such as "Version 1 option ... detected." Internally, the siunitx package now seems to use version-1-compatibility. Thus, you can achieve the same behavior, if you use \usepackage[version-1-compatibility]{siunitx} instead of the two lines of code you showed in your answer. However, Joseph Wright's answer is definitely preferrable.
    – leandriis
    Apr 25, 2021 at 7:40

To only get the units, you can do:


or (the more correct one):


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