[oligopoly]

10-15% and you have somewhat defined sixpack. Lower range of that continuously naturally and you might have yourself a problem. You only have to be somewhat enthusiastic about fitness and watch what you eat to get there. Not that uncommon these days

[brandonmenc]

Citation for 10% being dangerously low?

[ensiferum]

15% is pretty damn flabby though. Unless you have a very unique body composition and putting your fat into say your legs and butt (like women typically do) youll def have a soft doughnut around your waistline and no way you have six pack abs. Its more in the below 10% bf when you actually can start to dream about the 6pack if you actually have the muscle.

[oligopoly]

You've seen some misrepresented data. You commonly see fit people saying they have 6 or 8% fat % when they are closer to +12%. Most methods to determinate fat percentage are hilariously inaccurate. Look it up.

15% and you see hints of sixpack (clear outline) for most people who train.