How Many Spaces Go After a Period?

Put just one space after a period.

If you grew up using a typewriter, you were probably taught to put two spaces after a period (a practice called English spacing). But like the typewriter itself, that custom went out of fashion many years ago.

With modern word-processing programs, a second space is not only inefficient (requiring an extra keystroke for each sentence) but potentially troublesome: it can cause problems with line breaks.

In most cases, computers use proportional fonts so that a single keystroke creates the proper space between sentences. (When you're writing online, you'll find that many computer programs won't even recognize a second space.) In addition, there's no evidence that an extra space makes a document any easier to read.

Of course, if you're still using a typewriter, feel free to continue putting two spaces after a period. (And don't forget to change the ribbon now and then.)

Postscript: Spacing After Other Marks of Punctuation

As a general rule, put one space after a period, comma, colon, semicolon, question mark, or exclamation point. But if a closing quotation mark immediately follows any one of these marks, don't insert a space between the two marks. Here's how that looks in American English:

John said he was tired. Mary said she was "knackered." I said I was hungry.

In British English, as a general rule, knackered would be in single quotes (inverted commas) and the period would follow the closing quotation mark: Mary said she was 'knackered'. In either case, don't insert a space between the period and the closing quotation mark.

"Spacing around the dash [or em dash] varies," according to "Merriam-Webster's Manual for Writers and Editors." "Most newspapers insert a space before and after the dash; many popular magazines do the same, but most books and journals omit spacing." So choose one way or the other, and then be consistent throughout your text.