Number formatting: use of digit separators in manuscripts

I am reading through a manuscript that I am co-authoring with a colleague and I noticed that it used digit separators/marks for all the numbers (i.e. 2,500 instead of 2500). Maybe it's just me but I think this style started after my colleague started doing a post-doc in the U.S.

I have checked the author guidelines of a couple of journals that are likely submission targets in our field and they don't seem to include anything about decimal/digit separators. I also checked my previously published articles and noticed that numeric values were not edited (by press editors that is) to include digit separators.

Thus my question, is there a general rule-of-thumb regarding number formatting, especially considering digit separators?

• I don't think there are strict rules apart from journal-specific ones. I personally wouldn't put any separator. I'd use scientific notation for large numbers instead (2.5 x10^3). 2,500 was two and a half for me until I moved to the US. Commented Jul 31, 2014 at 13:53
• @Jigg: Scientific notation also carries some information about precision, e.g. 2.5x10^3 means "between 2450 and 2550". It's not really appropriate when exact integers are intended. It would look silly to write "Nature published its annual list of the year's 2.5x10^3 hottest organic compounds". Commented Jul 31, 2014 at 14:28
• @NateEldredge well it makes more sense to me than 2 and a half hot compound. (Joke aside, you have a point. Although I didn't know about this rule, I wouldn't assume the uncertainty if not explicitly given.) Commented Jul 31, 2014 at 14:52
• This depends on the field, publisher, journal, and country. When writing a paper, if you really care about it, look at the house style manual, which may or may not take a stance on it. The AIP Style Manual, for example, recommends using small spaces as separators. Other journals don't really say anything about it.
– E.P.
Commented Aug 1, 2014 at 13:53

Digit separators differ between countries, particularly since the decimal seprator is comma in many countries but a period in English/American. Hence in English you may use commas as digit separators while in other countries periods are used. Space is therefore the only separator that is not confusing. A general rule of thumb is to not use separators for single-thousands but start to use them for tens of thousands and up

1000

10 000

100 000

1 000 000

When using spaces in writing, it is good to remember to use non-breaking spaces so that numbers are not broken over lines.

• Assuming that the manuscript is written in Word (sad, I know..) does regular space count as non-breaking space? Commented Jul 31, 2014 at 13:54
• In Word you can use "Ctrl+Shift+spacebar" to get non-breaking spaces. Commented Jul 31, 2014 at 13:57
• ...in Windows. On a Mac, use option-space, in any application. Commented Aug 1, 2014 at 5:15
• In Word you can enter Unicode characters by typing their four-digit hexadecimal value followed by ALT+X. For example, U+2007 is a non-breaking figure space: 2007 ALT+X, and U+202F is a NARROW NO-BREAK SPACE (a good choice for the thousands separator in large numbers): 202f ALT+X. NB: Be careful when the character that immediately precedes the four-digit hex value is itself a valid hex digit: 33202f ALT+X (inserts a different character). As a workaround I do this: 33\202f ALT+X, then I delete the '\', then I continue typing. See also: jkorpela.fi/chars/spaces.html Commented Oct 18, 2021 at 1:29
• I would say that a space is the most confusing separator. Commented Mar 27, 2023 at 23:47

In scientific literature it is common to employ a thin space to separate groups of digits (see e.g. NIST SP811, §10.5.3). If you're using LaTeX to write your articles you can obtain this spacing in two ways:

1. Directly with the small-space command `\,`. For example: `There were \$10\,000\$ people at the concert last night` (well, not exactly a scientific example).
2. Using the siunitx package and the command `\num` (or `\qty` for quantities with units), which can take care of the spacing automatically. For example: `There were \num{10000} people at the concert last night` (it adds automatically a small space after the 10).
• I believe the `\,` operator works with or without the math mode being operational. Commented Jul 31, 2014 at 13:59
• Yes, you can get the small space both in text and math modes, but I prefer, for clarity, to have numbers written in that way delimited by the dollar signs. Commented Jul 31, 2014 at 14:02
• @aeismail you are right. As a reference, item one in this answer and this question: Behavior of \, in both text and math mode are helpful indeed. Commented Jul 31, 2014 at 14:04
• Always using math mode for numbers seems to stretch the notion of "math mode". So you would write `I was born in \$1983\$, and I live in \$02138\$ Cambridge`? Commented Jul 31, 2014 at 16:58
• @Sverre In simple cases like the ones in your example, I wouldn't use \$\$. In general, however, I'm used to employing systematically the features of the `siunitx` package: for typesetting most, almost all, numbers in my documents I use the `\num` command. In this way, I can change the formatting style for the whole document in one instance by means of the `\sisetup` command. For example, I sometimes need to change the decimal separator from `.` to `,` when translating from English to Italian and viceversa, and this can be obtained automatically. Commented Aug 1, 2014 at 7:18

I think that, in as much as there is such a standard, it tends to breakdown between scientific and humanities fields. In general, I would argue that the modern standard in science is to use only spaces as separators ("2 500" instead of "2,500" for instance), while the reverse tends to be true in the humanities.

However, the best guidelines for these sorts of issues, as usual, is to consult with the guidelines and recommendations of the individual publisher.

• so... if the journal has not specified anything it's free-for-all? Commented Jul 31, 2014 at 13:55
• @posdef: Basically, yes, so long as you're consistent! Commented Jul 31, 2014 at 13:57
• Let the typesetter worry about this. When putting together the manuscript for submission, worry about other things. Commented Jul 31, 2014 at 14:03
• @StephanKolassa: In case you were referring to a person by "typesetter": In some fields, authors are asked to provide a camera-ready document that is readily formatted for printing down to the letter. No further typesetting is done by the publisher, if it can be avoided. Commented Jul 31, 2014 at 18:52
• @StephanKolassa If you care about the appearance of your article, you should never let the typesetter worry about the typesetting details. When I receive proofs for my articles, more than half of my comments will be directed at the typesetter, asking him/her to fix typesetting mistakes or poor typesetting choices. Commented Jul 31, 2014 at 21:21