How do I pronounce "ratio 1:1"?

How do I pronounce "ratio 1:1"?

Should I pronounce it "ratio 1 to 1"?

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."

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."