Line numbers, page numbers, double spacing: what journals actually require.
Waraq · July 22, 2026 · RULE OF THE WEEK
Almost every journal wants line numbers, and most want page numbers next to them; double spacing is the part that varies. PLOS ONE tells authors to double-space the manuscript and to include page numbers with continuous line numbers. Frontiers in Neurology asks for the opposite spacing, a single-spaced document, while still requiring page and line numbers throughout. So treat numbering as close to universal, and treat spacing as a per-journal setting you look up in the guide for authors before each submission.
Why do reviewers care about line numbers?
Because a review is a list of specific objections, and every objection needs an address. "Line 214: this claim needs a citation" costs the reviewer five seconds to write and costs you five seconds to find.
Take the numbers away and the reviewer has two options. The first is to describe the location by hand: "in the paragraph beginning 'Although previous studies', on what I believe is page 9." Some will do that work. The second option, more common, is to compress the comment into something vaguer, and vague comments are the hardest kind to answer in a response letter. You end up defending a position the reviewer never quite specified.
Frontiers states the purpose inside the rule itself, requiring page and line numbers "in order to facilitate the review process." The double-spacing convention has an older logic. It comes from the years when editors marked up printed pages between the lines, and it survives because an annotated PDF still benefits from the white space. Whatever the history, both conventions now serve the same reader: the person writing marginal comments on your manuscript.
What does PLOS ONE require?
Three things at once: page numbers, continuous line numbers, and double-spaced text.
The submission guidelines put the numbering requirement in one sentence: "Include page numbers and continuous line numbers in the manuscript file." Spacing gets its own rule: "Manuscript text should be double-spaced."
The word continuous is doing real work there. Numbering runs from the title page to the final reference without resetting, so line 847 exists exactly once in the file. That is what lets a reviewer cite a line with no page attached, and it is one of the choices Word offers directly when you switch numbering on.
These items sit on the technical checklist that editorial staff run before an editor reads the science. A manuscript missing them typically comes back as a correction request, which resets your place in the queue for the sake of a two-minute setting. Format slips also tend to travel together with the substantive problems that get papers desk rejected, which is a correlation you do not want working against you on page one. The same guide fixes plenty else, from the 300-word abstract cap to Vancouver referencing, numbered in order of citation.
Does every journal want double spacing?
No. Frontiers in Neurology requires the reverse.
Its author guidelines read: "The entire document should be single-spaced and must contain page and line numbers in order to facilitate the review process." Same reasoning as PLOS ONE, same insistence on numbering, opposite spacing.
This is why there is no house format worth internalizing. Spacing behaves like abstract word limits, which also swing journal by journal: the only rule that binds you is the one in the guide of the journal in front of you. The practical risk is not ignorance but momentum. A manuscript rejected at a double-spaced journal and resubmitted to Frontiers arrives carrying the previous journal's layout, because nobody thought to recheck a setting that was correct last month.
If you write inside the journal's own template, the spacing usually comes preset. The check still takes one glance, so take the glance.
How do you turn these on in Word?
Three settings, each on its own ribbon tab: Layout for line numbers, Home for spacing, Insert for page numbers.
For line numbers, open the Layout tab, click Line Numbers, and choose Continuous. That single option satisfies the PLOS ONE wording. For spacing, select the whole document with Ctrl+A (Cmd+A on a Mac), then on the Home tab open Line and Paragraph Spacing and pick 2.0. For a single-spaced journal, pick 1.0 in the same menu. For page numbers, go to Insert, click Page Number, and choose a position; bottom center is never wrong.
Then scroll the document once. Selecting everything before you change spacing matters, because applying 2.0 with the cursor parked in one paragraph restyles that paragraph alone, and the mixed result looks worse than either setting applied cleanly.
How do you turn these on in LaTeX?
Two packages: lineno for the numbers, setspace for the spacing.
\usepackage{lineno}
\usepackage{setspace}
\begin{document}
\linenumbers
\doublespacing
For a single-spaced journal, drop \doublespacing and keep \linenumbers. If a journal ever asks for numbering that restarts on each page, load the package as \usepackage[pagewise]{lineno} instead. Page numbers need nothing; standard document classes emit them by default.
Two habits save trouble here. First, check whether the journal's template already loads lineno, since many do, and loading it twice with different options produces confusing errors. Second, skim the compiled PDF around display equations. The lineno package is known to skip numbering on some math lines, and its documentation carries the standard workaround if your manuscript is equation-heavy.
Which numbering do you pick when the guide is silent?
Continuous. A continuous number identifies a line by itself, which is the entire point of having numbers.
Per-page numbering makes every comment carry two coordinates, page and line, and both go stale the moment a revision reflows the text. PLOS ONE names continuous numbering outright, and most manuscript-format journals expect it. When the guide says nothing, continuous is the safe default; reserve pagewise numbering for the rare guide that demands it.
The wider habit is a formatting sweep before submission, with numbering and spacing at the top of the list because they are the cheapest items to fix and the first ones a technical check screens. A review that reads your manuscript against the target journal's own rule set, the way Waraq works, will quote "Include page numbers and continuous line numbers in the manuscript file" in the margin when the numbers are missing, which beats discovering the same sentence in a correction request two weeks later. The setting takes two minutes. The round trip through an editorial office takes days.