The woven fabric cannot be produced with any yam density as there is a maximum value of yarn sett which cannot be exceeded This limit depends on yarn geometry, properties, adjustments and type of weaving machine. Exceeding this limit causes increasing stresses on pans of the weaving machine and affects the quality of the woven fabric. Researchers tried to find out formulae to express this limit as a function of yarn type, yarn count and weave structure. They reached different formulae. Some researchers verified these formulae experimentally. They found that some formulae need correction. This paper aims to find mathematical formulae to express the maximum sect of yarns in the woven fabric as a function of weave structure and yarn diameters based on a geometrical model of the woven fabric. This paper presents also mathematical formulae of some quantities that depend on yarn sett such as weave angle yarn spacing, yarn crimp ratio, weave value, yam cover ratio, and fabric cover ratio. For practical application purposes two graphs are presented to determine maximum yam density (e.g weft density) The first graph gives the maximum set of plain or floated woven fabrics. The second graph gives the weave value of extended weaves in terms of diameter ratio and average yarn float. To obtain the maximum set in an extended weave, its weave value is multiplied by the maximum sett of the corresponding plain weave.