Size 39/40 (that’s about size 6 to 7 in the U.K. and size 8 to 9 in the U.S.); with modifications for other sizes

Because of the ribbing, this pattern is flexible and therefore can be used for smaller (i.e. children’s) sizes with the indicated number of stitches.

English version is here, updated 2023.
German version is here, updated 2023.