The spelling "percent" (one word) is generally accepted, I think. Thus I presumed that "permille" (one word) would be correct, but the Cambridge Dictionary only mentions "per mille". On the other hand, the MS Word spell check only accepts "permille" (the same is the case for the spell check in the editor on this site).

Google search seem to favor "per mille" and Wikipedia also uses that spelling, but mentions "permille" as an alternative.

So which is more correct? (and does there exist a good authoritative source apart from the SE users?)

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    encyclopedia.thefreedictionary.com/permille - The term occurs so rarely in English that major dictionaries do not agree on the spelling and some major dictionaries such as Macmillan do not even contain an entry. The term is more common in other European languages where it is used to express fractions smaller than 1%. One common usage is blood alcohol content, which is usually expressed as a percentage in English-speaking countries.
    – ColleenV
    May 5, 2021 at 14:05
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    According to Google Ngram, per mille is far more common than permille.
    – Void
    May 5, 2021 at 14:47

1 Answer 1


In English you say "per mile" or "per second" or "per dollar" or "per person" or ...

The phrase tells you to divide.

I have never seen "perAnything" other than "percent". That does mean "divide by 100". So "35 percent" is an everyday way to say "35/100" or "0.35".

"Per mille" would mean "divide by 1000". Most readers would not understand it, whether written as one word or as two. Small concentrations of drugs or contaminants might be described in "parts per thousand" or "parts per million".

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    Thank you. That the term is used rarely in English explains why it is difficult to find the correct spelling and why it may not have been adopted the same way as "percent". In my case, the context is technical so readers will have no problems understanding it, but I will keep in mind that "parts per thousand" may be more commonly understood.
    – nielsen
    May 5, 2021 at 14:13
  • You've never seen per thousand?? per is not divide by: it is for every
    – Lambie
    May 5, 2021 at 14:33
  • @Lambie Yes, "per" means "for every". It does not mean "divide by", it's an instruction to divide. To calculate your speed in miles per hour you divide the number of miles driven by the number of hours. May 5, 2021 at 14:36
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    Recognised spellings include per mil, per mill, permil, permill, permille, per-mille, per-mill, per-mil. May 5, 2021 at 15:01
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    @nielsen you seem to have found this answer helpful judging by your comment so you might like to accept it by clicking on the green tick (US=check mark) to indicate that.
    – mdewey
    May 5, 2021 at 15:29

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