You're asking and I'm answering . . .
"I was wondering how many crunches one is supposed to do daily for an effective workout. I've heard quality over quantity is important, but I have no idea whether the quantity should be 20 or 60!"
- Confused camellia2
I actually get this question a lot so to see my answer read more.
Unfortunately there is not a one size fits all answer. Trust me, I wish I could say, "Oh, just do 25," but I can't. So here is somewhere to start: beginners should do at least one set of as many repetitions as it takes to make the abs really burn and feel exhausted — then do three sets of however many reps leads you to feel the burn. For you this could mean five or 55 good, slow movements. It really depends on the level of the exerciser. I do know folks that will do 200 of the same ab exercise in one sitting, but I am not sure that's necessary (like you said, quality over quantity). Also, since our abs are almost always being worked when we exercise, I like to only have one day a week dedicated to my abs (along with cardio). You can do more or less, just make sure you give them time to rest and recover.
Now, that is not to say that you do one set of crunches and you're done once you feel the burn. If you really want to target your abs then you should repeat that process with your upper abs, lower abs, and obliques (and also do some back exercises if you really want to be complete). And as with any kind of strength training, push yourself by increasing your reps and once you get stronger.
Be sure to check out a few of my favorite ab exercises to get you well on your way.
Fit's Tip: Remember that you can build those abs nice and strong, but cardio is the only real way to get rid of the layer of fat covering them.