Skirt length is no trivial matter. The hemline and the length of this universally liked clothing requires quite a bit of deliberation. Afterall, the skirt is accepted as the best attire for women in even the most traditional and prestigious business places. Then there is the hemline index, linking economy to skirt length.
The so-called hemline theory which came up during the 1920s says "shorter the hemline, stronger the economy". This observation of the relation between hemlines of skirts and the economy is attributed to Wharton Business School Professor George Taylor. George Taylor in 1926 came up with a theory that suggests that hemlines on women's dresses rise along with stock prices.
In short, this means that during good economic times many women could afford silk stockings and hence raised their skirt hemlines. When economic conditions got worse the hemlines were lowered because they could not afford silk stockings
I cannot fathom why a tailor (instead of Mr.Taylor) did not notice this first. He deals the most with hems and hemlines.
How do we choose the hemlines
In a more ordinary scenario of our lives, the choice of the length of the skirt is more of a personal choice. You will be deciding on the skirt length according to many factors, other than personal choice - like the fashion of the times, culture, height, weight and shape of the person, personality, and comfort. If you are looking at short skirts one more important consideration comes into play - the shape and condition of your legs
Here is a post on choosing the right type of skirt for your body shape.
An extremely short skirt length, just covering the underwear. This is usually worn over hosiery.
Mini Skirt Length
This skirt length is at about 3 to 4 inches above the knee.
Street Skirt length
This skirt length is at or just above the knee.
Midi Skirt length
The skirt length falls between the knee and mid-calf.
This skirt length fall on the mid calf, about 6 to 7 inches from the floor. This length can make you look taller and thinner if the hemline comes about two inches above your ankle.
Ballerina Skirt length
This is a skirt length that falls just above the floor but reveals the ankle beneath. The hem can be right on the ankle bone, or just a few inches above, giving a glimpse of the ankle bone.
Floor Skirt Length
This is a skirt length that just grazes the ground or comes to about 1" above the floor with shoes. This is a dressy style more suited for evening or formal wear.
Handkerchief Skirt length
This is an asymmetrical skirt length with the high point at mid-calf and the low point falling to about the ankle
High Low skirt length
This is another asymmetrical skirt length, with the front portion shorter than the back - the front hemline will fall somewhere between the knee and the midcalf and the back will be longer.