The hemline is perhaps the most variable style line in fashion, changing shape and ranging in height from hip-high to floor-length. What is a fashionable style and height of hemline has varied considerably throughout the years, and has also depended on a number of factors such as the age of the wearer, the occasion for which the garment is worn and the choice of the individual.
Overview chart of changes in hemline height (skirt length), 1805-2005
In the history of Western fashion, the hemlines of the ordinary public clothes of upper- and middle-class women varied only between floor-length and slightly above ankle-length for many centuries before World War I. Skirts of lower-calf or mid-calf length were associated with the practical working garments of lower-class or pioneer women, while even shorter skirt lengths were seen only in certain specialized and restricted contexts (e.g. sea-bathing costumes, or outfits worn by ballerinas on stage). Things then changed in a previously unprecedented way. Hemline height is indicated as being at ankle length (or slightly above) at 1805 then dropping to floor-length 1835, where it stayed for most of the remainder of the 19th century (with a few temporary excursions back to ankle-length). During the mid-1910s, hemlines rose far above ankle-length relatively quickly -- and then in the mid 1920's (after a brief dip) rose almost all the way to knee length. 1927 saw "flapper length" skirts at the kneecap and higher, before shifting down again in the 1930s. During the period from the early 1930's to the mid 1960's, hemlines fluctuated in a zone which was quite different from the zone where hemlines had fluctuated during the 19th century. In the late 1960's, hemlines rose significantly above knee length for the first time. In the early 1970's, some women stayed with the miniskirt, some women went to the other extreme of ankle-length "granny dresses", while fashion designers tried to push an intermediate "midi" skirt length. The strong rejection by women of the attempt to impose the "midi" as the new norm marked the end of only one skirt-length at a time -- while fashion trends continued to come and go, from the 1970's on it was no longer true that a woman had to wear one particular socially predominating skirt length or be considered almost hopelessly unstylish. Instead, a variety of skirt-lengths now became acceptable (though after the early 1970's, the miniskirt itself didn't return as a mainstream fashion until the mid-1980's) -- and of course, in many contexts women are free to wear trousers instead of a skirt or dress. We are now living in an era of relative fashion freedom.
Another influence on the length of a woman's skirt is the Hemline Index, which, oversimplified, states that hemlines rise and fall in sync with the stock market.