A size 39 shoe on the European size scale is equivalent to a men's 6 or 6.5 in U.S. sizes. A size 39 is also equivalent to a women's size 8, 8.5 or 9.
The different measurement increments used in the two systems prevent a direct conversion of the European size to the U.S. size.
Shoe sizes in both Europe and the United States derive from the shoemaker's tool known as a last, which resembles a human foot. The differences between the sizes originate with the different measurement scales used by English and continental European shoemakers. U.S. sizes are modified from the English system.