Either of the ways that you show, but if you are spelling them as they are said, this is consistent: "zero point one percent" (written 0.1%) "one thousandth".
(written 1/1000 or 0.001)
You can also say "one part per thousand" (1 PPT).
ell.stackexchange.com/users/109772/Jack O'Flaherty
If you want a term similar to percent, but ten times smaller, it's per mille , denoted by ‰ sign.
So, 0.1%=1‰.
ell.stackexchange.com/users/4732/Ruslan
This question is part math, part language and part pronunciation.
You can say (pronounce) any of the following, because they are mathematically the same: A thousandth
One one-thousandth One out of a thousand .1 percent ("point one percent" or "one one-tenth of a percent") per thousand or one per thousand Others have mentioned 'per mille.'
That is not used in American English in my experience; it's based on French 'mille' meaning 'one thousand' (1,000).
ell.stackexchange.com/users/28413/user8356
That's a thousandth of something.
ell.stackexchange.com/users/8254/Mohamed Hamza
"1/100" is not one percent.
It's, one over one hundred .
"1⁄1000" is, one over one thousand.
Your question is, how do you say " .001 " and your second offering is correct : one thousandth .
You can also say, point zero zero one . "0.1%" you can omit the zero and just say, point one percent .
You can't say "one part per thousand" because we don't have the context of there being "parts".
Mathematical formulas can be vocalized (spoken aloud).
The vocalization system for formulas has to be learned, and is dependent on the underlying natural language.
For example, when using English, the expression "ƒ(x)" is conventionally pronounced "eff of eks", where the insertion of the preposition "of" is not suggested by the notation per se.
The expression " d y d x {\displaystyle {\tfrac {dy}{dx}}} \tfrac{dy}{dx}", on the other hand, is commonly vocalized like "dee-why-dee-eks", with complete omission of the fraction bar, in other contexts often pronounced "over" .
The book title
Why does E = mc2?
is said aloud as Why does ee equal em see-squared?.
–
Language of mathematics
ell.stackexchange.com/users/5117/Mazura
As a fraction, other answers have cover that well.
When one want to express “1⁄1000” like some percentage, one could say as below and even write using a single Unicode character.
Write as 0.1% and say "one tenth (of a) percent".
(Below are useful in select conversations - uncommon in general) Write as 1‰ and say "one per mille".
Write as 10‱ and say "ten per ten thousand".
Hmmm, too much like @Ruslan good answer.
Making it wiki.
ell.stackexchange.com/users/32004/chux - Reinstate Monica
An informal way to say it is "One in a thousand".
This kind of speech implies that it is either an estimate or intended as an exaggeration.
For a more exact number like 42/1000, "fourty-two out of a thousand" might be interpreted by the listener to be less precise than "fourty-two one-thousandths".
ell.stackexchange.com/users/115507/Greg
Speaking, I would say 'a thousandth' or 'a tenth of a percent'.
Using 'a' rather than 'one' in saying it seems nicer.
Further, in exposition, 'a' is an indefinite article, which indicates the speaker does not know the identity of the noun, in this case the thousandth in particular.
If you were speaking of a particular thousandth, perhaps the weight of sand which broke the camel's back then we would want to indicate we know that particular unit by using the definite article 'the' to say 'the thousandth pound of sand that broke the camel's back'.
Finally, if the unit of measure is the inch, a thousandth may be referred to as 'a thou' or 'a mil'.
ell.stackexchange.com/users/115630/Tim Rykken
In everyday language, people call "1/100" 1 percent. How do I say "1⁄1000"?    O point one percent  1 thousandth   or something else?
How do I say "1/1000"?
ell.stackexchange.com
<numbers><reading-aloud>
ell.stackexchange.com/questions/248151
ell.stackexchange.com/users/115410/shiqangpan
Speaking, I would say 'a thousandth' or 'a tenth of a percent'.  : You can also say "one part per thousand" (1 PPT) or you can say (pronounce) any of the following, because they are mathematically the same:   A thousandth   The following options are possible: "a thousandth", "one in a thousand", "one out of a thousand" and "one part per thousand".
The following options are possible: "a thousandth", "one in a thousand", "one out of a thousand" and "one part per thousand".