What length is considered cocktail attire?

The answer

Cocktail attire is usually knee-length or midi. Some hosts accept slightly shorter or longer hems if the fabric and styling look polished and elegant, and a floor-length gown is typically more than the occasion asks. Crepe, satin, lace and structured knits are common fabrics. If you are unsure, check the venue, the time of day and the invitation, and when in doubt dress one step toward the formal side.