One space after a full stop is the rule in every major style students use today: APA 7, MLA 9 and the Chicago Manual of Style. APA's sixth edition was the exception, recommending two spaces in draft manuscripts from 2009 until the seventh edition went back to one in 2019. If your instructor asks for two, give them two; otherwise use one, every time.
EdCitation publishes this guide. The history comes from a printer's manual of 1861, Chicago's first Manual of Style of 1906, a study of typing manuals in the Journal of Design History, and the style guides' own pages, all read in September 2026. Where we could read only a summary, we say so.
For your own paper, EdCitation's free Check your paper reads the style and formatting rules out of your brief, and Mechanics QA checks the finished file against the APA 7 student paper. The steps for clearing double spaces in Word are further down.
One space or two after a full stop: what does each style say now?
Every current edition asks for one space. The styles differ only in how firmly they leave room for an instructor who wants two.
| Guide | Rule now | What it says, in brief |
|---|---|---|
| APA 7 (2019) | One space | One space after a full stop or other end-of-sentence mark; follow an instructor or a non-APA publisher who asks for two (American Psychological Association, 2019) |
| APA 6 (2009) | Two spaces in drafts | Two spaces in draft manuscripts, while published work kept one (Wiederkehr, 2009) |
| MLA 9 | One space | One space unless the instructor prefers two; either way, be consistent (Modern Language Association, 2016) |
| Chicago 18 | One space | One space, for manuscripts and published work; the Press discourages two (University of Chicago Press, n.d.) |
| Your brief | Whatever it says | Both APA and MLA defer to the instructor; EdCitation's Check your paper finds the style the brief names |
APA's page on the rule points to section 6.1 of the seventh edition's Publication Manual and notes that the guidance changed from the sixth edition (American Psychological Association, 2019). The seventh edition's own summary of changes lists it among the mechanics of style (American Psychological Association, 2020). Chicago's editors have fielded the question so often that their Q&A keeps a whole topic on it, and one answer reports that no style they know of, APA 7 included, recommends more than one space (University of Chicago Press, n.d.).
Where did the extra space after a full stop come from?
It came from printing, not from the typewriter. For centuries, English-language printers set more space between sentences than between words, and typists later copied the printed page with the space bar.
Hand-set type: an em quad after the full stop
A compositor setting type by hand built each line from metal letters and blank pieces called quads and spaces. Henry Beadnell's Guide to Typography, a London manual for printers, told the beginner to put more space after punctuation, and "after a full-stop, an em quadrat" (Beadnell, 1861, p. 43). An em quad is a square blank as wide as the type is tall. The passage is in the manual's practical part, whose preface is dated August 1861; Harper (2020) dates the advice to 1859, the date of the first part.
The University of Chicago Press wrote the same rule into its first Manual of Style. Paragraph 245 asks for a 3-em space between ordinary words and "an em-quad after periods" and after question and exclamation marks ending a sentence (University of Chicago Press, 1906, p. 84). A 3-em space is a third of an em, so the gap between sentences was three times the gap between words. Harper (2020), who edits Chicago's online Q&A, points to wide sentence spacing in the 1611 King James Bible and the first edition of Sense and Sensibility in 1811; we did not examine those pages ourselves.
Typewriters and the typing manuals
Typing manuals turned the printer's wide space into a count of key presses. Walker (2018), writing in the Journal of Design History and drawing on her own list of more than 50 typing manuals and articles published between 1876 and 1981, reports that the earliest Pitman manuals asked for three spaces after a full stop, two after a colon or semicolon and one after a comma. Arthur Morton's manual of 1902 preferred two after a full stop, and that became the practice that lasted. Few manuals explained why; Walker notes that the rule followed the typesetting of the day.
The habit was taught hard. Walker (2018) cites Edith Mackay's Typewriting Dictionary of 1977, published by Pitman, as noting that a single space after a full stop would be penalised in typing examinations, at a time when most designers already regarded one space as correct.
The monospaced-type explanation, and why Chicago doubts it
A common story says typewriters needed two spaces because every letter on them takes the same width, so a single space after a full stop was hard to see. Harper (2020) calls this a myth: the wide space had been standard in printers' proportional type long before typewriters existed, so typists were imitating print, not correcting a weakness of their machines.
When did publishers and word processors go back to one space?
Printers moved first, typists decades later. Chicago's eighth edition of 1925 cut the gap between sentences to an en space, half an em, and the eleventh edition of 1949 asked for the same space after a sentence as between words (Harper, 2020). Harper suggests the Linotype and Monotype machines that replaced hand-setting "probably" played a part; that is his judgement, not a documented cause.
For typed manuscripts the change came later. The sample typewritten page in Chicago's thirteenth edition of 1982 shows two spaces; the fourteenth, of 1993, shows one; and the fifteenth, of 2003, was the first to recommend one space in so many words (University of Chicago Press, n.d.). Typewriters with proportional spacing had existed since around 1940, when IBM machines made them widely available (Walker, 2018). By the time students were writing on computers in proportional fonts, the publishing world had long set one space. The typing-class rule survived in the hands of people who had learned it.
Why did APA 6 ask for two spaces, and why did APA 7 drop them?
APA's sixth edition, published in 2009, recommended two spaces after each full stop in draft manuscripts. The APA Style Blog explained that the extra space broke text into chunks that were easier for markers and reviewers to read, while the usual convention for published work stayed at one (Wiederkehr, 2009). The seventh edition, in 2019, returned to one space, with room for an instructor or a non-APA publisher who asks for two (American Psychological Association, 2019).
We could not find a reason for the reversal on APA's own pages. The dates of both editions, and the other rules each changed, are in the history of APA Style. Johnson et al. (2018) describe the two-space rule as a change from a one-space requirement in earlier editions; we did not check the fifth or earlier editions to confirm that.
Do two spaces after a full stop make text easier to read?
Only slightly, and mainly for people who already type two spaces. The study that put APA 6's rule to the test came from Skidmore College's psychology department. Its three authors asked participants to type (to see which spacing they used) and then tracked their eyes as they read passages spaced each way (Johnson et al., 2018).
Their abstract reports that spacing made no difference to comprehension. The eye movements suggested that early processing of the text was easier with two spaces after a full stop, and those who type two spaces themselves gained the most. The authors took this as support for APA 6's recommendation, which the seventh edition overturned a year later.
The effect was small. Chicago's Q&A quotes the article's conclusion: two spaces raised overall reading speed only for two-spacers, by about 3%, and the authors add that period spacing is not worth passionate argument (University of Chicago Press, n.d.). Chicago's own view is that there is no definitive proof an extra space improves readability, and that preference for it is probably familiarity.
What we could not read
The full article is behind a paywall. We read its abstract in PubMed and the conclusion as Chicago quotes it, so the number of participants and the typeface used are not given here. If you cite the study, read the full text through your library first.
How do you handle sentence spacing in an assignment?
Use the spacing your brief or your named style asks for, and make it consistent. In order:
- Learn which style governs. EdCitation's free Check your paper takes the brief as a file or as pasted text and shows the style it names, quoting the sentence that named it. How to read an assignment brief covers the rest of the brief.
- Apply that style's rule. APA 7, MLA 9 and Chicago all want one space. If the brief itself asks for two, the brief wins: APA and MLA both say so.
- Distrust old handouts. A guide written for APA 6 will still say two spaces. Columbia College's library guide for APA, updated in March 2026, still tells students to put two spaces after a sentence's full stop and only one in the references (Columbia College, 2026). If a guide and the brief disagree, ask the person marking.
- Clear the double spaces in Word, as below.
- Check the whole file. Mechanics QA checks font, spacing, margins, headings and the reference list against the APA 7 student paper, and lists the slips it finds.
Replacing double spaces in Word
Microsoft's own steps for Word on Windows start at Home > Editing > Replace (Microsoft, n.d.):
- Open Replace. On a Mac, Microsoft gives Control+H for the basic Find and Replace pane.
- In Find what, press the space bar twice.
- In Replace with, press it once.
- Select Replace All. Microsoft suggests Replace rather than Replace All if you want to review each change, which is wise if your paper aligns anything with spaces.
- Repeat until Word finds nothing: three spaces become two on the first pass, then one on the next (Harper, 2020).
Word's wildcards can do it in one pass. With Use wildcards ticked in the advanced Find and Replace, the pattern {n,} finds at least n of the character before it (Microsoft, n.d.), so a space followed by {2,} finds every run of two or more spaces. Harper (2020) gives [ ^s]{2,}, which catches non-breaking spaces too.
What a real brief tells you, and what it does not
We pasted the paper guidelines for an MIT OpenCourseWare course, Global Africa: Creative Cultures, into Check your paper on 26 September 2026 (Edoh, 2018). It returned seven rules, each beside the sentence it came from: Times New Roman, 12 point, double line spacing, a target of 5 pages, 1,250 to 1,500 words, "Chicago" as the citation style, and a reference list. It set aside two sentences it could not turn into a rule, the argument the paper must make and the questions on writing quality.
Two things to note. The brief names "Chicago Citation Style: Footnotes and Bibliography", and the checklist recorded only "Chicago", so read the source sentence it shows you: EdCitation's Cite a source builds Chicago 18 author-date, not footnotes. And the brief says nothing about sentence spacing, so no rule appeared. When a brief is silent, the named style decides, and Chicago asks for one space.
Where does EdCitation fit?
EdCitation reads the brief, finds and cites the sources, and checks the finished file. It never writes any part of a paper, and it never changes a space in yours: the spacing is fixed in Word by you.
Mechanics QA (Pro, $8 a month, see pricing) goes through a finished Word file or PDF rule by rule. It holds the typeface, line spacing, margins, headings, title page and reference list to the APA 7 student paper, finds comments or tracked changes a marker should never see, matches citations to references, and catches figures that disagree and slips a spell-checker misses. Among its mechanical slips it flags a double space between sentences, after a letter, a figure, a bracket or a closing quotation mark, and it counts each one. We tested it on a short file with four double-spaced sentence breaks, after a word, a year (2018), a closing quotation mark and an abbreviation in capitals (USA). It reported "4 mechanical slips: double space." and advised "Find & Replace the slips; read the flagged paragraphs once more." It does not look in the reference list. Use Find and Replace for the spaces, and Mechanics QA for everything else.
Cite a source (free, no account) is the best tool for the reference itself, because it builds the entry from the publisher's record rather than writing one, which no chatbot can promise. Given the study's DOI, it returned this APA 7 entry from Crossref's record:
- Johnson, R. L., Bui, B., & Schmitt, L. L. (2018). Are two spaces better than one? The effect of spacing following periods and commas during reading. Attention, Perception, & Psychophysics, 80(6), 1504–1511. https://doi.org/10.3758/s13414-018-1527-6
It needed no correction: the title is in sentence case, "The" after the question mark is capitalised as the start of a new sentence, and the journal and volume are italic. It also screens the source for retraction, and this one is not retracted.
Find sources (free) searches about 300 million published works. Asked for typing manuals and the history of document design, it put Walker's article first and her 2014 chapter on house style and typing manuals third. A claim written as a sentence, "two spaces after a period make text faster to read", did not bring up the Skidmore study in its first 100 results; "spacing after periods during reading" put it first. If a claim search misses, try the words a title would use. Then check your finished list in Verify references, free.
Quick questions
Does APA 7 want one space or two after a period?
One. APA 7 asks for one space after a full stop or other mark ending a sentence, unless your instructor or a non-APA publisher asks for two.
Did APA 6 require two spaces after a period?
It recommended two spaces in draft manuscripts, from 2009 until the seventh edition went back to one in 2019. Published work kept one space throughout.
What does MLA say about spaces after a period?
MLA asks for one space after a full stop or other concluding mark unless your instructor prefers two, and for the same spacing throughout.
Why did typists use two spaces?
Because printers had long set a wide space between sentences, and typing manuals copied it with extra presses of the space bar. Early Pitman manuals asked for three; two became the lasting rule.
How do I remove double spaces in Word?
Open Replace, put two spaces in Find what and one in Replace with, and select Replace All until nothing is found. EdCitation's Mechanics QA then checks the rest of the file's formatting against APA 7.
References
- American Psychological Association. (2019). Spacing after a period. APA Style. https://apastyle.apa.org/style-grammar-guidelines/punctuation/space-after-period
- American Psychological Association. (2020). Guide to what's new in the Publication Manual of the American Psychological Association, seventh edition [PDF]. APA Style. https://apastyle.apa.org/instructional-aids/whats-new-7e-guide.pdf
- Beadnell, H. (1861). A guide to typography, in two parts, literary and practical; or, The reader's handbook and the compositor's vade-mecum: Part II. Practical. F. Bowering. https://archive.org/details/guidetotypograph00beadrich
- Columbia College. (2026, March 18). Formatting your paper. APA Style Guide. https://gocolumbia.libguides.com/c.php?g=338877&p=2282177
- Edoh, M. A. (2018). Paper assignment guidelines [Course materials, 21G.026 Global Africa: Creative Cultures]. MIT OpenCourseWare. https://ocw.mit.edu/courses/21g-026-global-africa-creative-cultures-spring-2018/pages/assignments/paper-assignment-guidelines/
- Harper, R. (2020, March 24). One space or two? CMOS Shop Talk. https://cmosshoptalk.com/2020/03/24/one-space-or-two/
- Johnson, R. L., Bui, B., & Schmitt, L. L. (2018). Are two spaces better than one? The effect of spacing following periods and commas during reading. Attention, Perception, & Psychophysics, 80(6), 1504–1511. https://doi.org/10.3758/s13414-018-1527-6
- Microsoft. (n.d.). Find and replace text in Word. Microsoft Support. https://support.microsoft.com/en-us/word/training/find-and-replace-text-in-word
- Modern Language Association. (2016, July 27). How many spaces should I leave after a period? MLA Style Center. https://style.mla.org/number-of-spaces-after-period/
- University of Chicago Press. (n.d.). One space or two? [Chicago Style Q&A]. The Chicago Manual of Style Online. https://www.chicagomanualofstyle.org/qanda/data/faq/topics/OneSpaceorTwo.html
- University of Chicago Press. (1906). Manual of style: Being a compilation of the typographical rules in force at the University of Chicago Press, to which are appended specimens of types in use. https://archive.org/details/manualofstylebei00univrich
- Walker, S. (2018). Modernity, method and minimal means: Typewriters, typing manuals and document design. Journal of Design History, 31(2), 138–153. https://doi.org/10.1093/jdh/epx018
- Wiederkehr, S. (2009, July 30). On two spaces following a period. APA Style Blog. https://web.archive.org/web/20250707193442/https://blog.apastyle.org/apastyle/2009/07/on-two-spaces-following-a-period.html