will you literally say 99.99% word by word？Or there is a usual abbreviation ？

Yeah we'd say that, it's a mouthful but that's normal when heavily emphasizing and exaggerating something small note is most people would probably say "ninety nine point nine nine" instead of "ninety nine point ninety nine"

I would and have said it as “ninety nine point nine nine percent”

Yes. Reading it out loud I would say “ninety-nine point nine nine”

Word for word it's ninety-nine-point-nine-nine-percent. Yeah I'd say it completely for the emphasis.

No 99.99% of people use numbers instead of the words

I think most people will say the digits to the right of the decimal individually. ninety-nine point nine nine percent.

Yes you would but most people would say 99% not 99.99%

There is a regular phrase "Five Nines" which means 99.999% and is used in technology settings all the time to refer to uptimes (only 5 minutes of down time in a year). Saying "Four nines" would play off that phrase and be useable here but its not a common phrase. But then again 99.99% isn't either, usually in English speech (vs writing) we would only say 99% chance it was an honest mistake not 99.99%.

You read out every digit of a decimal individually

yes, everything is written correctly and would actually say "ninety nine point ninety nine"

From Amazon Reliability, they say X nines, for example [https://aws.amazon.com/blogs/publicsector/achieving-five-nines-cloud-justice-public-safety/](https://aws.amazon.com/blogs/publicsector/achieving-five-nines-cloud-justice-public-safety/)

I say How you say it in the beg, at the end, I say point nine nine I’ve been speaking English my entire life I am from the usa

The numbers after the decimal should be pronounced individually, so you would say "point nine nine".

Yes. It's being used for hyperbole here so I would emphasise the "ninety nine point nine nine" as well.

The reason you would not say "ninety nine point ninety nine", is because decimals can be as many digits long as you need. For instance 99.99 is the same as 99.990, so now should you say nine hundred and ninety at the end? we have infinitely long numbers like pi, 3.15159... because I could say however mamy digits, I cannot say three point one hundred and fifty one, because then if I want to add one more digit I would have to restart with one one thousand, five hundred and 15. To get around both of these issues, after the decimal place it makes the most sense to just say the numbers in order.

Imo English speakers would replace it with "almost certainly" or similar instead of saying 99.99%

If one wants to be precise, it is "ninety nine point nine nine," not "ninety nine point ninety nine." 

Yes, I would say it like this: "ninety-nine point nine nine percent". It's for emphasis.

"One to million chance" since "one to one hundred thousand" is too long for me

Colloquially, I would say " ninety-nine point ninety-nine percent." I would say "Ninety-nine and ninety-nine hundredths" if I was being graded on correctness.

The most formally correct way to read this number is: “ninety-nine and ninety-nine hundredths percent” with the *and* specifically and redundantly indicating the decimal place. But nobody talks that way, probably not even your math teacher, so you’d expect almost anyone to read it as: “ninety-nine point nine nine percent.”

one in ten thousand chance of the opposite but thats just me

Ninety nine point nine nine

It is unlikely that one would phrase the sentence with four 9s if spoken rather than written. There is not a typical abbreviation for general English use. Various engineer disciplines may use "four nines" to refer to "99.99%" in discussions about reliability, for example "Youtube had four nines availability in the last decade."

yup. though you say the numbers behind the decimal individually (weird math rule :/) so this would be ninety nine point nine nine, 7.64 would be said seven point six four etc etc

Nyndi nine poinine

Numbers after the decimal point are pronounced individually, so read out loud this would be: "ninety-nine point nine nine percent" If someone was speaking but not reading text aloud, and was just trying to communicate "almost guaranteed," they'd probably pick a number that doesn't take as long to say, like 99.9%

If there are few decimals like this, I usually just say it completely. If there are many decimals or I feel lazy, I say ninety-nine point nine repeating.

Yes, kind of. I personally wouldn't say it, but "there is a 99.99% chance" is emphatic in two ways. First, there's the reason why you say out "ninety-nine-point-nine-nine-percent" (note that the only "ninety" comes before the decimal point-- at least the way I learned math, more on that later). You say all those extra words so that it takes longer. I hate it because the speaker is wasting my time to be emphatic. If the speaker has a reputation for being good at gauging probabilities, then they shouldn't need the extra words. If the speaker has a reputation for being bad at gauging probabilities, then the extra words aren't going to help. The second way "99.99%" is emphatic is in the idea that percentages are a concept that Smart People use. The speaker is trying to hint an air of academia or prestige about their claim by using percentages. It's bullshit; percentages aren't difficult math, and the speaker has no experimental basis for saying "99.99%" as opposed to "99.9%" or "99.999%", even though the probability of the inverse differs by a factor of ten. As someone who bothered to learn basic math (and this is very basic math), and who uses basic math on a daily basis, I'm going to think less of the speaker in this situation for using the trappings of precision to be emphatic about their stupid gut feeling. The speaker is wasting words AND claiming a level of precision that doesn't exist. As for "ninety nine point ninety nine" versus "ninety nine point nine nine," the way I learned math, you put individual digits after a decimal point. "Point three hundred" is needlessly confusing: it could be ".300", as the decimal point indicates that digits are being bumped to the right, but it could also be "30.0", as the "hundred" in "three hundred" bumps the "3" two spaces to the left. That's how it works to the left of the decimal point, after all. 3 is three, and 300 is three hundred. The way I learned it, to the right of the decimal point, you should just rattle off the digits, not bothering to group them into tens, hundreds, etc., unless you're expressing the decimal as a fraction (".003" can be expressed as "three thousandths", for example). Saying out, "Ninety nine point ninety nine percent" doubles down on the idea that the speaker only remembers a few words from elementary school math class rather than any actual math concepts.

I would say a "ninety-nine point nine nine percent chance"

Yes, out loud, "ninety nine point nine nine percent". And the more nines after the "point" the more confidence in the result you are emphasizing.

I might be a little wild for this but I don’t say “ninety nine point nine nine percent,” but “ninety nine point ninety nine percent” or just “ninety nine percent”  cause the whole thing is too long to say most of the time. I’m not saying that this is what everyone or even a large majority of people will do, but it’s what I do and you might encounter others who do that.

If I bother writing it that way, certainly. Well, at least ninety-nine point nine-nine percent of the time. I read decimals one number at a time and say "o" for 0

That's how I would read it aloud, but I wouldn't choose to say it that way absent the text. "Ninety-nine point nine" is fine, but "ninety-nine point nine nine" is too long to say - I'd probably say something like "it's overwhelmingly likely that this was an honest mistake" instead.

If I said this out loud I would just say “ninety nine percent” because it gets my point across and it’s less work than saying “ninety nine point nine nine”.

I say ninety-nine dot nine nine out of habit due to uni, but before that i did used to say point

Yes, you would say the whole thing like that, but it's rather cliche and a bit cringey. Better to say something like "near certain" or "almost guaranteed". When you say something like "I would say..." you are making a guess at something. To immediately follow that up with a very specific number like "99.99%" is contradictory.

basically, it's just feeling. If ya wanna do 99.99%, do that if ya wanna add some 9s? Why not if ya wanna go down some 9s to 99% or even 90%? Why not all of it basically means "I am sure this will happen" without actually saying "it's going to happen."

Yes, you say "ninety-nine-point-ninety-nine-percent chance that.."

In technology you might say "4 nines" instead, but this is fairly niche and only really when talking about [availability ](https://en.m.wikipedia.org/wiki/High_availability#Percentage_calculation)

I think most people would say ninety nine point nine percent. The extra 9 doesn't add much

Usually people ramble a random number of 9s to indicate near certainty. Usually it's more than 2 in speech and exactly 2 in writing.

It’s a common error to express the digits after the decimal point this way. “…Point nine nine” is correct, but “…point ninety nine” isn’t. That’s just maths, not particularly a language thing.

Would* you say not Will you say

If the number is representing an actual quantity, anything before the decimal point is read as a normal number, after the point the number are just said in order. So 1234.5678 would be "one thousand two hundred and thirty four point five six seven eight". In the context of this sentence the person is trying to emphasize that something is very likely. It kinda of ment to be a bit of a mouthful to emphasize how sure the writer is about how likely the thing is.

Just commenting to say that while “ninety-nine point nine-nine percent” is *technically* correct, “ninety-nine point ninety-nine percent” is imo completely colloquially acceptable and understandable and is what I, a native english speaker, would say in a casual setting like this. Anyone who would argue otherwise is splitting hairs. eta since this is an english learning subreddit: for anyone who doesn’t know, “splitting hairs” means you’re arguing about minor & unimportant details

nanny nine nanny nine

This is usually said by either douche-bags on the internet or scientists/biologists/doctors that want to make it very clear that everything has a chance to fail (see birth control). So it's said in its entirety to clearly make the statement.

Yes, we normally literally say it out. There is an abbreviation in technical circles that just counts the number of nines.  If a material is 99.9% pure it’s called “three-niner” grade.  If Google is shooting for 99.995% uptime reliability some people say “four and a half niner”.  But that’s how engineers put it, not the general public. 

Ninety nine point 9 repeating would be acceptable as well