A pair of jeans labeled size 29 generally equates to a U.S. size 8 or 10, depending on the manufacturer. The 29 indicates a 29-inch waist size, but even this measurement is not always precise.
Sizing standards vary wildly among manufacturers, and a size 6 from one brand might fit similarly to a size 10 from another. In addition, some brands practice "vanity sizing," in which smaller sizes have larger dimensions to flatter customers into believing they comfortably wear smaller sizes than they truly do. Trying jeans on before purchasing is the best way to ensure a good fit; if purchasing online, consult a size chart to determine the right size based on waist size and inseam length.