How do I pronounce 3/21?

Question

I need some help. So, I have been doing some work with fractions, and this came up: 3/21. I have no idea how to pronounce the 21 part. Is it twenty-oneth or..? I have no clue, so can someone give me the correct pronunciation?

Apart from /2 "halfs" and /4 'quarters' (in the UK) (many Americans say 'fourth/fourths') we say the denominator (lower number) as the singular or plural for of the ordinal number, so 1/21 is "one twenty-first" and 3/21 is "three twenty-firsts". Alternatively you can say "numerator over denominator" so "three over twenty-one". — Michael Harvey, Jan 25 '21 at 14:03
I see above I wrote 'halfs'. The plural of 'half' is 'halves'. — Michael Harvey, Jan 25 '21 at 14:43
This might help: Is there a standard way to read aloud fractions? — ColleenV, Jan 25 '21 at 15:33
You can always be a nerd like me and say "zero point one, four, two, nine" (3/21 == 0.1429) — Jonas Benz, Jan 26 '21 at 13:32

Ethan Bolker · Accepted Answer · 2021-01-26T15:00:05.427

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How you say it depends on the context.

If it comes up in a discussion of mathematics you would say "three over twenty-one". Since you asked while you're thinking about fractions that's the answer.

In everyday speech, that or "three twenty-firsts" would do. (I wonder where it might come up in everyday speech.)

Of course 3/21 = 1/7, so "one seventh" might work too.

When you get to algebra and want to talk about (ax+b)/(cx+d) you have no other way than to say "a x plus b over c x + d".

edited Jan 26 '21 at 15:00

answered Jan 25 '21 at 15:05

Ethan Bolker

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"a x plus b over c x + d" could also mean "ax + b/c + d" or "(ax+b)/(cx) + d", right? Or would they be described differently? – Eric Duminil Jan 26 '21 at 15:06
@EricDuminil A mathematician hearing that would implicitly put the parentheses in the right place. If the other were intended the speaker would have to say so. – Ethan Bolker Jan 26 '21 at 15:25
Dictating an equation over the phone, you'd need to find a way to make it explicit. Reading an equation aloud as you write it on the board, to help people read your writing or reduce how often they need to look up and back down to their notebooks, more ambiguity is acceptable. – CCTO Jan 26 '21 at 17:05
@EricDuminil There is clearly room for ambiguity. But it's like BODMAS, the ambiguity isn't there because people agree to a standardized meaning. – user117065 Jan 26 '21 at 18:45
The examples given for a mathematics discussion vs. everyday speech are precisely reversed. Given the question is about pronunciation, I don't see the relevance in saying something like, "30 is pronounced thur'-dee," simply because many people colloquially pronounce the Ts as Ds. The pronunciation of 3/21 is nothing but "three twenty-firsts," which is also more common in a technical discussion. – benJephunneh Jan 26 '21 at 18:47
...and of course if you're a Brit it's "three on twenty-one" rather than "over". – Lee Daniel Crocker Jan 26 '21 at 19:34

score 8 · Answer 2 · answered Jan 25 '21 at 17:38

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In mathematics, the numerator is always pronounced as a cardinal number and the denominator is always pronounced as an ordinal number. This answer may be helpful for further clarification.

So the pronunciation should be "three twenty-firsts." In common speech, though, you could say, "Three out of twenty-one," or something similar. You will even hear from some people, "Three on twenty-one," or "Three by twenty-one."

answered Jan 25 '21 at 17:38

benJephunneh

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Please avoid three by twenty-one, as this often means three multiplied by twenty-one. – Peter Jan 26 '21 at 07:56
You may also simply hear ‘three twenty-one’. Usually this indicates that it’s meant to be a date without a year though, and not a faction, ratio, or proportion. – Austin Hemmelgarn Jan 26 '21 at 12:46
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Is "three on twenty-one" a regional variant of "three over twenty-one" (or vice versa)? – David K Jan 26 '21 at 13:04
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I'm a mathematician and "three twenty-firsts" sounds a bit ornate to me. It would almost surely be more common to hear it as "three over twenty-one", unless in very formal contexts perhaps. – lukeuser Jan 26 '21 at 13:53
lukeuser, certainly, even English professors and authors never hear and often do not use correct grammar when speaking casually. :P Does this change what the correct answer is, though? – benJephunneh Jan 26 '21 at 18:37
First point: there's not a clear line between what is correct and what most people do with language. I'm not convinced anyone would say pronouncing the fraction as "three over twenty-one" is incorrect. It's just in a more relaxed style than "three twenty-firsts". – lukeuser Jan 29 '21 at 23:52
Second point: when you said "in mathematics, [...] the denominator is always pronounced as an ordinal number", did you mean that it is always correctly pronounced as such? Because I took it more literally and though you were actually commenting (incorrectly) on usage. – lukeuser Jan 29 '21 at 23:56
Luke: 1. I would agree with you if you said there is not always a clear line. There very often is a readily distinguishable line that makes it easy to say whether the common usage is correct. I think, however, you're reading too much into the statement that one way is correct. While cardinal/ordinal is the rule, I don't view it as a grammatical rule that implies cardinal/cardinal (or whatever your preference is) is wrong. There are very many conventions in mathematics that exist for the sake of ease of communication, not because they are correct. Still, the convention is what is taught. – benJephunneh Feb 01 '21 at 07:51
Luke: 2. It seems as if you're saying there should be a caveat to the statement, "...always pronounced...," that warns people that the rule is not always followed, but I actually did devote a second paragraph to describe to the English-language-learner that they should expect to hear fractions pronounced differently from the rule. I'm puzzled that you suppose my first statement asserts the usage follows cardinal/ordinal. Again, that is merely the rule/convention. I suppose I could edit my answer to say, "In mathematics, the convention is to pronounce...." – benJephunneh Feb 01 '21 at 08:06

score 1 · Answer 3 · answered Jan 26 '21 at 23:18

For Dates

If it's a date rather than a fraction, a US speaker would likely say "three twenty-one" when the context was clear, or "March 21st" if the context were not unambiguously a date. In American English (the military being a notable exception) the standard numeric format for dates is typically dd/mm/yy or dd/mm/yyyy. Absent other cues, I'd assume 3/21 is a date and say it that way.

For Fractions

Other answers have addressed fractions, so I can add little there, but "three twenty-firsts" or "3 out of 21" would not be uncommon ways to express this conversationally. However, this is simply unlikely to come up often in casual conversation as the number of items that come in packs of 21 is...well, I can't even think of one offhand.

In conversation, I'd usually expect to hear "I'll have three of those [uncounted items]" or (assuming it's a cake or pizza in 21 slices) "I'll take three slices, please!" without reference to what fraction of the whole that represents. Numeric precision isn't generally required in casual contexts, but your situation may differ.

How do I pronounce 3/21?

3 Answers3

For Dates

For Fractions