I would like to ask about a concentration unit. What does it exactly mean when stock concentration of something is, for example, 5X?

Thank you in advance!

  • $\begingroup$ To me, this has nothing to do with concentration or units in general. "5X" is probably a dilution factor or just poor typography. If you have the label scanned, feel free to post the image here to make the question more clear. $\endgroup$
    – andselisk
    Commented Mar 26, 2019 at 13:19

1 Answer 1


The “X” factor simply indicates that the solution is in a concentrated form that must usually be diluted to a “1X” concentration for use. For example, a 5X concentrated solution must be diluted 5-fold, while a 100X concentrated solution must be diluted 100-fold. The dilutions are usually done using water.

See more here under part 3:


  • 1
    $\begingroup$ Often, it is followed by the abbreviation of a solution commonly used in a biochemistry lab, such as PBS (phosphate buffered saline) or TE (tris EDTA) or sample buffer (for SDS gel samples). Of course, it means nothing unless you know the composition of these solutions. $\endgroup$
    – Karsten
    Commented Mar 26, 2019 at 17:40

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