Taking my first and last typing lessons back in 1980, I learned that we put two spaces after a period before starting a new sentence. Well, 1980 was a long time ago.
You could argue either way, one space or two, but it really doesn’t matter as long as your consistent. AP style indicates that you should just use one space after a sentence. I believe Chicago style says to use two. When writing online you should use just one space, and I have a very good reason for it.
Why Use Just One Space Online?
The reason you want to use just one space after a period when writing online, is because it could make life a whole lot easier for you in the future. When it’s time to upgrade your database, you can thank me then. Time to time, upgrades to servers occur. Whether we do it to improve performance, enhance security, or simply move the changes will happen. What runs on the server? The database.
When contents of a database are moved or if the database has been recently updated to the latest software, all double spaces within your content could get converted to special characters. Ready to edit every webpage or article on that website? The easy way to avoid this? Just use one space.
I had a little reminder of this after updating a clients server, and their database. All of there content is dynamic, drawing from a database. The problem for me? They doubled space after every sentence, leaving me with a mess of cleanup. Doh!
Looking at it from a usability perspective we need to remember what the general audience is already used to. Some of the most viewed pages today are undoubtedly the portals like Yahoo, Microsoft, and Google. What is popularly read on those pages? News. What format is news usually distributed? AP style, and AP style uses single space. So to give users what they are already used to, use single space.
Double space or single space after sentence? Online, make it single space.