A model for optimization of fiber-coupled diode-laser end- pumped solid-state lasers, which describes the pump beam by its M2 factor, is proposed. Using the mode-overlap integrals of a four-level laser, numerical investigations were carried out to obtain the pump beam optimum focusing conditions that ensure a minimum threshold pump power and a maximum mode-matching efficiency at a given laser beam spot size. For the purpose of design simplicity the numerical data were fitted with analytical functions of laser mode volume, pump beam M2 factor, and active medium absorption efficiency at the pump wavelength. With a simple output-to-input power relation, these formulas provide a straightforward procedure to design the optimum laser resonator and the coupling optics and to determine the expected output power. To show the model utility a Nd:YAG medium, end-pumped with fiber-coupled diode-laser systems of different M2 factors, was considered. A good agreement between experiments and theory was obtained.