Big difference, actually. And it’s not because one has an ‘m’ while the other sports an ‘n’. LOL.
EM DASH: is roughly the size of an ‘m’, and sometimes called a double hyphen (–). It is used to indicate an added emphasis, interruption, or abrupt change of thought. It is also used (sparingly, I hope) to replace colons, semicolons, commas, and parentheses.
e.g. I like you—really like you—for being a good friend. [added emphasis]
She dashed off to go to the party—but wait, she forgot her purse. [interruption]
“I know, but—” The baron picked up his gloves. “—this plan of yours is sure to fail.” [interruption]
I wish you would—oh, never mind. [abrupt change of thought]
In most Word documents, you can create an em dash by making a double hyphen (–) and pressing ENTER. Word automatically converts it for you. Also, there are no spaces in between the word prior to the em dash, and the word after it.
THIS: party—but
NOT: party — but
Em dashes also precede quotation attributions.
e.g. A professional writer is an amateur who didn’t quit.
—Richard Bach
EN DASH: is traditionally half the size of the em dash, or is roughly the size of an ‘n’. It is technically wider than a hyphen (-). They’re used to:
1. Connect a range (such as numbers).
e.g. 1–10
pp. 35–40
Non-numerical range:
e.g. January–December
2.To contrast values, or illustrate a relationship between two things.
e.g. Father–daughter event
Boston–Hartford route
3. When combining open compounds:
e.g. a high school–college conference
These are the simple definitions—we could probably get even more technical and discuss other aspects of the em dashes and en dashes, but unless you’re writing formally, these will do.
You can find more about this topic here and here and here. Also, I found a wonderful blogpost by M.E. Summer of Sticking to the Story about hyphens. Check it out here.
Questions? Comments? Any info you’d like to share? Please use the comment section. Thanks!
Precy Larkins 
Ask and I shall receive! Haha! Thank you for posting this. Phew! Glad to find out I've been using them right (well, usually). ;o)
Great post. I sometimes use the em-dash more than I should, but it is so very useful.
Angela, this was for you, as requested. =)Sarah, hey, you still need to email me so I can send you your gift card!
I feel like I just went back to English class … and my head hurts now.*I tease*Thanks for the postie!
Whew! Girl, you are so GRAMMAR SAVVY. We might have to rename you the Grammar Queen. No worries … you can still keep your sparkly vampire crown, too. LOLThanks for the great reminder!
Haha! I was only answering Angela's request. 😉
I'm sure this is one of those things where every style book gives you a different opinion, but for interruptions I've always followed the Chicago Manual of Style, which differs slightly from your description. Per Chicago (6.90, for those following along at home :-)):"I know, but"—the baron picked up his gloves—"this plan of yours is sure to fail."If you mean for the dialogue to be interrupted by the action, it would be slightly different:"I know, but—" The baron faltered as he picked up his gloves. "This plan of yours is sure to fail." The sick part is I knew exactly where in Chicago to look (15 years as a copyeditor to thank!). And the even sicker thing is that this is waaaaaay more fun than revising. You can't tell I'm procrastinating, can you? 🙂
Thanks! This is just what I needed! 🙂 Another question I don't have to ask! LOL
That's good info, Jenny. I don't have the Chicago manual; I should get one. There are so many variants, depending on the source. I also read somewhere that copyeditors will have their own preferences, so I guess if we're at that point (our ms going through copyediting and proofreading stage) they'll change it anyway. Thanks for the heads up!Rene, glad this was helpful! 😉
Thanks! I can always use these tips. Sharpening the saw.
Cherie, I think after you're done with "Hidden" you should collect all of your writing 101 posts and put them in downloadable book format. I always have trouble with the hyphens, because I want to put them into my writing way more than they need to be there. Thanks for a great post!Scott
You are tagged :)http://innerowlet.blogspot.com/2011/05/writing-is-not-like-box-of-chocolates.html
Thanks for helping me with EM and EN Dash. I was a bit confused regarding their usage.
@Shelly: Hi and thanks for stopping by!@Scott: Haha. I don't know how to make downloadable books. For now, I'll just keep them all in one page as a resource. =)@AM: Aahhh! I'm IT! =)@Rachna: Glad I could help. ")
Ahh!! I love dashes!!! I didn't know there were two kinds though. Once I took an essay to the writing center and the guy looked at my paper and then at me and said, "You really like dashes, don't you?" I hate commas, so anywhere I can use dashes and use them right, I will!!
This was amazingly helpful! Damn those dashes!
I'm an em-dash addict. Although your post helped me with the en-dash, which I never use.