What body fat percentage does a woman need for flat abs?

Flat abs: Well, that's sort of difficult to answer because there are so many body types out there. You could have flat abs at 10%, 20%, and 30% body fat depending on how your fat is distributed. Some people carry their fat in their thighs/buttock, while others carry it in their midsection. So, body fat% doesn't really dictate if you have flat abs or not. Work on your abs and don't think about % body fat.