So many options. So tempting to type a hyphen, hit the space bar, type another word and see your hyphen magically turn into an en dash. No one will notice …
But an en dash just isn’t an em dash, is it? It’s shorter.
  • Em dash: 
  • En dash: –  
  • Hyphen (for size): –

Historically, the en dash and em dash names are derived from the width of a lowercase and uppercase M, respectively, in commonly used typefaces.

An em dash (—) can be used in pairs to encompass a word, phrase or clause within a sentence. They can also be used to separate one part of a sentence from the main body, and they are particularly useful in long, complex sentences.
An en dash (–) means “through” and usually connects a closed range of values like dates and numbers: Feb. 15–28 or Page 19–345.
And in case you’re wondering if an en dash should have spaces around it: It depends on the application, but usually when connecting two numbers, spaces should be left out.
—Sarah Muench