Dictionary.com Word FAQs
What should be the spacing between sentences?
Traditionally, students in typing classes have been taught to put two spaces between sentences. In typewritten texts, one space between words was fine, but two spaces seemed necessary to make the break apparent. To be strictly accurate, only one standard word space should be inserted between the end of one sentence and the start of the next. However, strict application of this rule in the world of automated composing systems can cause readability problems, because several factors affect how the spaces appear in the composed text. The issue of spacing between sentences should be decided for individual typing jobs, not applied across all projects as a standard. If readability won't suffer, only one space should appear between sentences; if readability is an issue, two spaces can be used. Whichever choice you make, ensure that it is implemented uniformly throughout the text.