These days, most publications recommend using just one space.
I hear your groans. Your complaints: “but I’ve always” or “I like the distinction between sentences/thoughts that two spaces offer.” There are any number of other reasons to oppose the change.
So why switch from one space to two spaces?
Well, for one thing, it’s the new rule. You’ll find these major style guides recommend one space after a period.
The Chicago Manual of Style
US Government Printing Office Style Manual
The Publication Manual of the American Psychological Association
Changing won’t be hard. It’s just a matter of retraining that thumb to live in a one-space world. You can do it.
Using a word processor, you can correct spacing on already written documents with the search-and-replace function. To make the spacing permanent for future word documents, click on the Grammar/Style option, then select the option one space after the period.
Once you’ve retrained yourself or reset your word processor, typesetters (yes, typesetters still exist) and formatters will love you. You’ll cut their workload. Now, every time they find two spaces after a period, they must delete one of the spaces.
You can see more about the whys of the change from two spaces to one here.
Will you break the rule or embrace the new rule?