I would like to redefine the electron mass unit in siunitx so that it is \mathrm{m}_0 instead of the default \mathrm{m}_\mathrm{e}. How do I do that?

  • \DeclareSIUnit{\Electronmass}{\mathrm{m}_o} and \si{Electronmass}
    – user11232
    Nov 28, 2014 at 10:17

1 Answer 1


The definition of \electronmass is


Just change it.




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However, you must realize you're changing a standard symbol. And this shouldn't be done.

  • Even if I do not change a standard symbol and give it another name, your approach looks weird when I have an exponent for my unit, e.g. $\SI{2}{\electronmass^2}$ (the original symbols have that too...). Is that intentionally (and by this I mean should it be that way due to some convention)?
    – DaPhil
    Dec 1, 2014 at 7:22

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