This study measured maxillary sinus volume as an aid in determining the volume of graft bone needed before grafting autogenous bone to the maxillary sinus floor. Maxillary sinus volumes were measured from computerized tomographic images of 38 sinuses using a 3-dimensional reconstruction system. When the sinus-lift procedure was simulated, volumes (mean +/- SD) of the inferior portion of the sinuses were 4.02 +/- 1.44 cm3 for 15-mm lifting and 6.19 +/- 1.77 cm3 for 20-mm lifting. In bone grafting of the maxillary sinus floor, taking into consideration individual differences in maxillary sinus volume and resorption of the grafted bone, 5.46 cm3 or more were required for a 15-mm lift and 7.96 cm3 or more were required for a 20-mm lift.