I've been learning how to use FontForge and am now getting my feet wet with kerning. I see that there are two options to do kerning: classes and pairs.

To me, classes seem to have no downside. When I'm setting a 'T' to a 'c', 'e', and 'o', I can do them all at once! If I have something that's a bit of an oddity, like an 'a' or an 's', I can just set it by itself (knowing too that once I get into diacritics those characters won't be alone anymore).

So, why would I use pairs at all? Is it just a legacy thing since pairs came before classes? Does setting up a class introduce a lot of overhead into the font file that can bloat it or slow it down?

  • this is a guess, but it may have something to do with setting up contextual ligatures ?
    – MephistonX
    Commented Apr 30, 2013 at 8:08

1 Answer 1


pairs are generally more accurate than classes but take longer to create (obviously). classes are the most popular and the difference is negligible, but if you want perfection and a real "optical" look as oppose to a "mathematical" look, use pairs.

  • is it right that kerning classes inherit its kerning from the upper class, which means i can give more than one class to a character or pair?
    – codelio
    Commented Apr 30, 2013 at 22:05
  • not sure. i think you can determine where the inheritance comes from but why would you want to give more than one class to a pair? Commented Apr 30, 2013 at 22:10
  • because i thought so inheritance is possible: lets say for all g,p,q,y,∫.. following an "schuster" T or F but on top a class which has different Kerning with W's for the same g,q,..
    – codelio
    Commented Apr 30, 2013 at 22:26
  • How do you the determine which class has priority? Can you actually do this in FF? Commented Apr 30, 2013 at 22:31
  • very good question, will test this.
    – codelio
    Commented Apr 30, 2013 at 22:38

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