Hmm, this is hard. I think I recall from a gazillion years ago when I had to take two costume design courses as a theater major that hemlines around that time varied from mid-calf to halfway between the knee and the sole of the foot. I remember this vaguely because I was supposed to draw a dress like that, and since I have less than no ability for drawing, it was nearly my downfall in the class. 
I am realyig on my vague memory about this, so it's a tough call between 6-8 inches. I guess I'll go with 8, hesitantly.
This thread is fun for me because I like reading others' responses AFTER I've posted mine, and NOT researching the question online. Cool!
@Aquarius "What will Mrs. Thompson Say" is always hard for me.
I understand and enjoy the Victorian Era way of thinking and fashion.
The Edwardian period succeeded by the King George V era is very foreign to me. I have made some progress with understanding Mrs. Thompson view of the world in 1919. Prince Edward, Duke of Windsor is only in his 20’s.
I have high hopes for 1920.
