Updated: Dec 17, 2021
Photo: an example of proofreaders' marks for inserting a hyphen, an en dash, and an em dash.
Most people use hyphens on a regular basis, but what about en dashes and em dashes? I didn't even know what they were until I went to university, and I wasn't familiar with how to use them until I took a grammar course for my Editing Certificate. So what are the differences between a hyphen, an en dash, and an em dash?
A hyphen is the shortest dash, and there is a key for it on standard computer keyboards (in North America). Hyphens have multiple uses but one key use: they form some compound terms such as low-key and up-to-date.
Hyphens can be tricky when it comes to compound terms because sometimes hyphens are necessary and sometimes they are optional. For example, there is a difference between a small animal clinic and a small-animal clinic; the hyphen in that phrase changes the phrase's meaning. In a small animal clinic the animal clinic is small, but in a small-animal clinic the clinic specializes in small animals. However, with phrases like well meaning or well-known, hyphens are optional depending on the situation and the style guide.
Hyphens are also used with some prefixes and suffixes such as in ex-girlfriend and in some compound terms (e.g., this is a how-to-use-punctuation blog post). Grammar Girl goes much more in-depth about hyphen usage in "How to Use Hyphens in Your Writing."
The Chicago Manual of Style seventeenth edition also has a wonderful hyphenation guide.
En dashes are named as such because the dash is the width of the letter N. En dashes are used in number and date ranges, and they sometimes replace hyphens in compound terms.
There is no en dash key on a standard computer keyboard, but MS Word has an autocorrect function that changes two hyphens into an en dash if there is space on either side. On a Mac, you can also use the keyboard shortcut option + hyphen to make an en dash.
For more information on en dashes, check out Grammarly's "When Should I Use an En Dash?"
Em dashes are named as such because the dash is the width of the letter M. Em dashes are more common than en dashes, although there is still no key for them on computer keyboards. You can make an em dash on MS Word by typing two hyphens together with no space on either side. On a Mac, the keyboard shortcut for an em dash is option + shift + hyphen.
Em dashes offset parenthetical material or indicate interruptions in speech (e.g., Her article—which was about punctuation—helped writers and editors alike). Check out Grammar Girl's article about "When to Use—and Not Use—an Em-Dash."
Although many people are unaware of the differences in these dashes, they make a difference in how people read sentences. Dashes can affect how a reader understands a word or phrase, and knowing how to use a hyphen, an en dash, and an em dash is a useful tool for your writer's toolkit.