Collection efficiencies of two types of impactor nozzles were calculated for spherical particles and fibers. The flow field through the impactor was calculated for Reynolds numbers of 100 and 1100 using a finite element method. Equations of motion for spherical particles and fibers were obtained and were used along with flow held information to calculate impactor collection efficiencies. The calculated collection efficiency for spherical particles agreed with that in the literature. The cutoff size at 50% agreed with experimental data, but the collection efficiency curve lacked a long tail at low collection efficiencies. For fibers, collection efficiency curves were obtained in terms of fiber Stokes number and aspect ratio. The calculated collection efficiency curve moved to higher Stokes numbers with increasing fiber aspect ratio. The cutoff size for fiber minor diameter decreased as the fiber aspect ratio increased.