EY and Avhaben, the Shulchan Aruch says (OC 75:1) that a tefach in a place that it is the way of women to cover is erva. The Rema brings down that there are those who say that less than a tefach by a woman not his wife is erva. The Mishna Berura says (seif katan 7)some say that the upper leg is erva even less than a tefach even his wife (the Chazon Ish seems to be meikal on these points).What these yesh omrims mean in a practical situation is for a rav to decide.
Popa, if you mean that I have a history of looking up things on websites and then checking them I plead guilty. What is wrong with that? Do you think that anyone remembers where exactly where every source is found even if he knows that they exist? That is why Hashem gave us search engines.