The jump-to-contact phenomenon of atomic force microscopy measurement is investigated. The force-approach relation for the adhesive contact based on the Lennard-Jones potential with the Derjaguin approximation is analyzed. For a small Tabor parameter, the force-approach relation is similar to that with the van der Waals force between two rigid spheres. For a large Tabor parameter, the force-approach relation is similar to that with the van der Waals force between two deformable spheres. Empirical formulas for the approaching part of the force-approach curve are proposed. The jump-to-contact distance can be obtained by using the semi-empirical formulas. The jump-to-contact distance for a fixed grips device and for large Tabor parameter is also obtained.