#en dashes

I assume some of this confusion may arise from a particular formatting feature in Microsoft Word. If you're using the default settings and you type a parenthetical hyphen in Word (where "parenthetical" in this case means you're using the hyphen, with spaces on either side of it, between two words in a sentence, to set off a clause or something similar), then after you've finished typing the word following the hyphen, Word will automatically change your hyphen to an en dash for you. So you end up with an en dash even though technically YOU typed a hyphen. But even though Word is doing this for you automatically, that doesn't make hyphens and en dashes the same thing – and  you can tell they're not the same thing because they're not the same length, as illustrated by my handy side-by-side comparison above.

There also seems to be confusion over what these little lines are used for. Here's what I've learned in my experience as a writer, through 11 years of post-secondary education and a further 6 years as an academic, and in over 3 years as a full-time copy editor for one of the biggest academic journal publishers in the world (where a large part of my job consists of changing dashes to the right kind):

Hyphens are used to hyphenate – i.e., they are used in compound words, such as "great-aunt".

En dashes can be used in two ways: parenthetically as punctuation within sentences – like this – or to separate numerical/chronological ranges, e.g., 16–22, January–March, Cambrian–Devonian, etc. Note that when en dashes are used parenthetically, they should have spaces on either side of them, whereas when they are used within ranges, there should be no spaces. (And, contrary to some of the posts I've seen going around, it is not anything about the spaces that defines whether you have an en dash; it is simply and entirely the length of the dash that defines it, not the presence or absence of spaces.)

Em dashes, to my knowledge, are ONLY used as punctuation in sentences, either to set off parenthetical information or to indicate that narrative or dialogue has been abruptly terminated. Here are some examples: 

I know this is boring—at least, I assume it is—but it's really useful to know this shit.

"Wait," John shouted. "What are you—" The rest of his cry was drowned out as the monster threw up on his head.

Unlike en dashes, em dashes NEVER have spaces before or after them, even when used parenthetically in exactly the same way that en dashes can be used.

Whether you use en dashes vs. em dashes for parenthetical stuff is entirely up to the publisher (if there is one), your teacher (if this is for school) or you (if you're in charge of formatting decisions). In my experience, em dashes are more popular for parenthetical use in North America, and en dashes are used more in this way in the UK, but it really does vary. If it's up to you, use whichever you prefer for the parenthetical stuff; just be consistent. (And please do use hyphens to hyphenate and en dashes for ranges.)

And, finally, some keyboard shortcuts. If you have a Mac, like I do, here's how you type these marks:

Press the "-" key once for a hyphen. That's the key with two horizontal lines on it on the upper right of the keyboard, between the zero key and the +/= key.

Press the same "-" key while holding down the "option" key for an en dash.

Press the same "-" key while holding down both the "option" and "shift" keys for an em dash.

(I guarantee there are also keyboard shortcuts to type all three of these marks with a PC; I just don't happen to know what they are. Feel free to add this info in the comments if you're a PC user.)

Thanks for reading. I hope this is useful. And please, please help stop the abuse and misrepresentation of these innocent marks! :P

tl;dr

Hyphens, en dashes, and em dashes are NOT the same thing; they are 3 lines of different lengths (shortest = hyphen; medium = en dash; longest = em dash).

En dashes sometimes (not always) have spaces on either side of them; hyphens and em dashes never have spaces. 

Hyphens hyphenate.

En dashes separate ranges (with no spaces) or are used parenthetically (with spaces).