In text type, it’s important to realize that there is only one space after a period. The two-space habit after a period can be tough for many typists to break; however, those two spaces can tell some people a lot about your inexperience and your age. Plus, those double spaces often create more work for others, unless you are creating documents in mono-spaced fonts.
The reason for the double space is that in typewriter fonts (or mono-spaced fonts like the one shown), all of the characters are alloted the same width of space, whether it’s an “m,” an “i,” or a period. The two paces after a period calls attention to the punctuation mark at the end of each sentence and creates a visual pause that is needed. In digital typesetting, however, the fonts are variably spaced, meaning each letter is encoded with its own space that is different based upon the width of the character. The punctuation is designed to be slightly larger so that it is easily recognizable at small point sizes without that double space. Therefore, one space after a period has been the standard in typeset copy for some time. Stop using double spaces, as you create more work for your editor or graphic designer when they have to go in and remove those extra spaces.