The pronunciation/spelling-out of "1:1" is "one to one" or "one-to-one.
" I just wanted to add that you wouldn't say "ratio one-to-one.
" You would either say "a ratio of one-to-one" or "a one-to-one ratio."
english.stackexchange.com/users/1606/Claudiu
In speech this is obviously always pronounced "ratio one to one."
In writing, it is a matter of style.
Anything of a technical nature should always be written in the 1:1 form, but when writing prose, fiction or something informal, you should certainly consider writing it as it would be spoken: "The mix was applied in a one-to-one ratio."
The use of hyphenation and words instead of numerals makes the sentence flowing and readable, and encourages the reader's eye to see this as a single, commonly-occurring term.
Note that for the purpose of clarity ratios should generally be stated in the same clause and the same order as the two sets being compared: "Boys and girls were present in a ratio of 3:2."
english.stackexchange.com/users/1542/PyroTyger
You would pronounce it "a ratio of 1 to 1", but it's worth noting that there are sometimes exceptions.
In films and photography , for example, ratios such as 16:9 and 4:3 are often described as "16 by 9" and "four by three", respectively.
english.stackexchange.com/users/603/Django Reinhardt
Hmm, not sure how correct this is
but I read a:b as "a is to b".
And a:b::c:d as "a is to b as c is to d".
Probably British English (else it's Indian :))
english.stackexchange.com/users/124/Autodidact
I am Indian and I say 1:1 "one to one" and a:b::c:d "a is to b as c is to d".
english.stackexchange.com/users/18710/Narendra
In the United States, "one-to-one ratio" is preferred.
A pronunciation of "ratio" is given at the following.
https://www.youtube.com/watch?v=_yVnFCNMchA
In addition, The American Heritage Dictionary shows both a two-syllable and three-syllable pronunciation for ratio. https://www.ahdictionary.com/word/search.html?q=ratio
english.stackexchange.com/users/336461/Kevin
How do I pronounce "ratio 1:1"?  Should I pronounce it "ratio 1 to 1"?
How do I pronounce "ratio 1:1"?
english.stackexchange.com
<pronunciation><numbers>
english.stackexchange.com/questions/3713
english.stackexchange.com/users/1503/aneuryzm
You would pronounce this either as "a ratio of one-to-one" or "a one-to-one ratio". The pronunciation is "one to one", using the word order "Ratio one to one".In the USA, it is a three-syllable pronunciation according to US American Heritage Dictionary. In writing, the presentation of "ratios" is an issue of style. Colons must be used, but where words are used instead of numerals, this can make reading easier. Hhowever word order of sets must be respected to understand the concept as in "Boys and girls were present in a ratio of 3:2." It is to be remembered, that ratios are expressed differently in the photographic and cinema domains as in 16:9 is described as 16 by 9.
You would pronounce this either as "a ratio of one-to-one" or "a one-to-one ratio". You would either say "a ratio  of  one-to-one" or "a one-to-one ratio." The use of hyphenation and words instead of numerals makes the sentence flowing and readable, and encourages the reader's eye to see this as a single, commonly-occurring term.  
This is pronounced as "One-to-one". You would pronounce this either as "a ratio of one-to-one" or "a one-to-one ratio".
The pronunciation is "one to one", using the word order "Ratio one to one". In the USA, it is a three-syllable pronunciation. In writing, it is an issue of style. The colons must be used, but using words instead of numerals can make reading easier, however word order of sets must be respected to under the concept as in "Boys and girls were present in a ratio of 3:2." Ratios are expressed differently in the photographic and cinema domains. In the world of film and photography different descriptions are used for ratios.
You would either say "a ratio  of  one-to-one" or "a one-to-one ratio." The use of hyphenation and words instead of numerals makes the sentence flowing and readable, and encourages the reader's eye to see this as a single, commonly-occurring term.  
You would pronounce this either as "a ratio of one-to-one" or "a one-to-one ratio".