There are three categories of dashes: hyphens (-), en dashes (–) and em dashes (—). What's with the weird names? Well, en and em refer to the letters 'n' and 'm' respectively. In a given font, much of the distinction of width is based on the width of the 'm' since it is the widest letter in the alphabet. Therefore an em dash is the same width as the letter 'm' for a specific font. The same goes for an en dash, which is usually about half the width of an em dash (since the letter 'n' is generally half the width of the letter 'm'.)
That said, here are the guidelines for when to use these different dashes:
Hyphens separate compound adjectives or hyphenated words
Examples: small-business owners or Pre-Raphaelite
En Dash (–)
En dashes substitute for the word “to” when writing dates
Example: January 15 – 17, 2010
Note that there is a space on either side of the en dash.
Em Dash (—)
Em dashes separate the start of a sentence from the text when listing bullet points
- Visual Communicators—Art Directors, Graphic Designers, etc.
Em dashes also help when a list of items separated by commas contains additional commas that would make it difficult for the reader to understand:Okay, that's great, but all you see on your keyboard is a hyphen key right? Well you need to know a few commands to make en and em dashes happen and unfortunately it varies based on the program, but no worries, we have the short cuts listed below.
(… the key Great Lakes states—Wisconsin, Illinois, Indiana, Michigan, with the longest coastline of all, Ohio and Pennsylvania—have all agreed …).
Note that there is no space on either side of an em dash.
How to type en and em dashes:
PCs—for Microsoft Word (and most other PC word processing programs)
Typing a word followed by a space, two hyphens, another space and then a word will result in an en dash: word – word.
Typing a word followed by two hyphens and then another word with no spaces either side of the hyphens yields an em dash: word—word.
Macs—for Adobe Creative Suite programs and anything within Mac OS
Key command: Alt/Option + - (hyphen)
Key command: Shift + Alt/Option + - (hyphen)
**Please also note that a hyphen is not the same as the minus symbol. There is a separate glyph to use for this so that it matches the plus sign. (Thanks for the tip, Suzanne!)