I'm working on a copy editing project and in the copy they use

...only nine and one-half kilometres long...

I have decided the hyphen is wrong. However one half sounds awkward to me. Is that just because of usage? So I'm wondering: are both nine and one half and nine and a half correct? Or is one more formal? In the end, which is preferred?

  • 2
    If one is being mathematical, "nine and one-half" would be correct. For "ordinary-people-speak" "nine and a half" would flow a bit smoother. Neither is incorrect, and the hyphen in "one-half" is optional if not being formal/mathematical.
    – Hot Licks
    Oct 24, 2014 at 21:23
  • Stupid Modern English. Just a millennium ago we'd have laughed about this question, when a and one sounded the same and meant the same thing.
    – RegDwigнt
    Oct 24, 2014 at 21:49
  • 1
    Well, you can only ever have one half. Any more, and you'd have one, and one [or more]! It is very old-English to say "... and one half", modern communication follows that "... and a half" is normal. Use that one. It's not a matter for formality either.
    – KyranF
    Oct 24, 2014 at 22:01
  • If you adopt the simple rule that all numbers associated with standard measures of length, weight, and volume should be given as numerals (or decimals), you can go with "only 9½ kilometres long" or "only 9.5 kilometres long," depending on which form you use elsewhere in the project. This obviates not only the hyphenation question but the "a half" versus "one half" issue.
    – Sven Yargs
    Oct 29, 2014 at 7:17

1 Answer 1


Regarding the hyphen, you can find a discussion here:

Why does "one half" have no hyphen, but "two-thirds" does?

which clarifies this issue.

Regarding "one half" vs "a half," either are acceptable. It would appear that "one half" is more formal, but "a half" is more popular, not surprisingly as formality has become uncommon these days. :)

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