When writing is it correct to use numerals (e.g. 1,2,3,) or spell out the number (e.g. one,two,three)?
2There is no general rule in English. This is governed by style (essentially typography), not orthography. The only time you have to be careful about it is formal publication (i.e. not a blog but a periodical or book), and in that case, you should investigate, determine, and adhere to whatever style guidelines govern that publication (eg the Chicago Manual of Style, AP, etc). The editors will help you ensure you're playing by the rules.– Dan BronMar 6, 2016 at 0:01
1To reiterate what @DanBron writes, it's not even that there are fixed formal rules that you need not apply in the vast majority of circumstances: even when there are rules they will entirely differ from place to place, and only really exist for the sake of consistency within a publication and to avoid arguments.– Dan SheppardMar 6, 2016 at 0:58
My own custom is to spell out one-word numbers, which are easier to parse mentally, and to use the numerals for two-word and larger numbers; i.e., to spell one to twenty, thirty, forty, and so on, but to use numerals for 21, 22, 23, 57, 101, and so on.– AnonymMar 6, 2016 at 4:33
In my long ago technical writing class I was taught to spell out one to nine and use numerals for 10 and above. I don't remember how we were to treat zero, but I'd guess we were supposed to spell it out.