I learnt that chazal wrote “Shok b’isha ervah” – “the leg of a woman is ervah” (area that must be covered). The knee and above must be fully covered at all times front and back per basic halacha (Shok b’isha ervah) so this typically means a skirt with at least 4 inches below the knee so that it is covered even when sitting, getting up, into a car or walking outside in a bit of a wind. Below the knee it must be covered in stockings per poskim who say chazal are referring to below the knee or otherwise the accepted Orthodox practice, which you halachicly cannot deviate from.
Another terrible problem lately is ppl wearing low necklines or tight fitting clothes.