I need to express things like (longhand) 'this fullword contains the elapsed time in units of 1048576 microseconds'.

I would imagine something like '... units of µs × 2²° ...' (horrid superscript, I know) might be an adequate shorthand, and thought of siunitx:

%In units of \si{\mebi\micro\second}. % <= Fails

In units of \si{\mebi\bit}.

In units of \si{\mebi\second}.

In units of \SI{1}{\mebi\second}

It appears that siunitx, reasonably, won't let me mix prefixes:

! siunitx error: "prefix-base-mismatch"
! Prefix bases do not match.

Can anyone suggest an adequate notation, and how I might achieve it in siunitx?

  • 4
    What's wrong with 'in units of \SI[parse-numbers = false]{2^{20}}{\micro\second}'?
    – Joseph Wright
    Commented Jun 11, 2012 at 16:18
  • 1
    How about \DeclareSIUnit{\microsecond}{\ensuremath{\mu}s} \si{\mebi\microsecond}?
    – Jake
    Commented Jun 11, 2012 at 16:29
  • @JosephWright: Nothing. An excellent suggestion! Commented Jun 11, 2012 at 16:43
  • @Jake: I like that slightly better than Joseph's, as it gives me the flexibility of producing 'Miµs' (as in mimsy). If you'd like to make that an answer, it's got a good chance. After Joseph has had another opportunity to comment. Commented Jun 11, 2012 at 16:46
  • 4
    @Jake That will use the wrong symbol for micro (italic rather than upright by default). If you want to go this way, use \SIUnitSymbolMicro rather than \ensuremath{\mu}.
    – Joseph Wright
    Commented Jun 11, 2012 at 17:09

1 Answer 1


You can use

\DeclareSIUnit{\microsecond}{\SIUnitSymbolMicro s} \si{\mebi\microsecond}

which allows you to type

In units of \si{\mebi\microsecond}.

to get


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