There's something I've noticed more and more recently while reading copy around the internet: the double space after a sentence.
Here's a quick PSA for anyone reading this: You only need one. It doesn't matter what you learned in school—the single space is backed up by nearly every style guide out there. But there are more reasons than that to avoid the double space.
A Brief History of the Double Space
The double space is an artifact left over from the days when we were stuck writing on typewriters. Thanks to spacing issues inherent in typewriters, two spaces were essentially used to help differentiate one sentence from the other. (Which explains why you tend to see older writers favor the two spaces over one—it's how they learned.)
We're not stuck on typewriters anymore. Modern word processors figured out the spacing issues, and that eliminated the problem altogether.
Deciding Whether You Fit the Exception
To be fair, there is still some merit in using two instead of one, as research has found there is a slight increase in reading speed. A study at Skidmore College determined two spaces after a period increases reading speed by about 3%—equivalent to about nine extra words. (Disclaimer: This study is under intense scrutiny because they used a monospace font, meaning each keystroke receives an equal amount of space.)
However, that doesn't mean you should start using it.
The reason behind the double space was technology that is now outdated. If you use it now, your typography will make you look behind the times—which could turn some prospects away.
That's not to say there's never a reason to use the double space. If your brand has a very specific aesthetic (for example, I'm picturing a retro-infused microbrewery that uses Courier New in all of its copy), the double space could be part of your brand's fingerprint.
Cleaning Up Your Double Spaces
So, what do you do if you have a bunch of web copy that includes a ton of double spaces? You may want to get your IT team involved if you have a lot of copy to review, but the answer is the same no matter what: seek and destroy.
Using Ctrl+F to bring up your search function, then hit the space bar twice to isolate your double spaces. If you've got any, use the Replace tool by inserting a single space, and then hit the Replace button.