This is a question about skirt lengths. From this answer:
The halacha is that "tefach b'isha ervah" - a tefach (about 3.5 inches) uncovered on certain parts of a woman's body is ervah - nakedness. (B'rachos (24a) in the name of Rabbi Yitzchak). The arm must be covered at least to the elbow and the leg must be covered at least to the knee.
Rabbi Getsel Ellinson (Woman and the Mitzvot: Volume 2) - Pg. 186, note 37, writes that it is probably okay to pray as long as there's less than a tefach uncovered above the elbows and knee. However, it is certainly absolutely forbidden to pray in the presence of a woman whose skirt does not cover past the knees when she is sitting down, because the skirt will not cover ervah.
My question is as follows: if opaque stockings (tights) are worn under a skirt, may the skirt then be any length? Would a skirt that hits more than a tefach above the knee be acceptable in this case (presuming that the skirt falls within the bounds of aidelkeit and concern for the local standards)?