When should I use an em-dash, an en-dash, and a hyphen?

Question

I generally know how to use a hyphen, but when should I use an en-dash instead of an em-dash, or when should I use a hyphen instead of an em-dash?

Answer 1

An em-dash is typically used to act as a comma or parenthesis to separate out phrases—or even just a word—in a sentence for various reasons (i.e. an appositive). Examples where an em-dash should be used:

• School is based on the three R’s—reading, writing, and ’rithemtic.
• Against all odds, Pete—the unluckiest man alive—won the lottery.
• I sense something; a presence I've not felt since—

An en-dash is used to connect values in a range or that are related. A good rule is to use it when you're expressing a "to" relationship. Examples where an en-dash should be used:

• in years 1939–1945
• pages 31–32 may be relevant
• New York beat Los Angeles 98–95
• Olivia Newton–John

A hyphen is used to join words in a compound construction, or separate syllables of a word, like during a line break.

• pro-American
• cruelty-free eggs
• em-dash
• it's pronounced hos-pi-tal-it-tee

Finally, a minus sign − is distinct from all three of the above.

• 4 − 2 = 2.

If you want to use the correct dash or hyphen in StackExchange comments, just use the appropriate HTML entity: — for em-dash, – for en-dash, and − for the minus sign. The hyphen is, of course, on directly your keyboard.