ABSTRACT Models for the forces required to remove a fixed volume of rock with a single cutter have been applied to different polycrystalline Diamond Compact (PDC) bit designs. The integration of the forces for each cutter over the bit face gives the torque and weight-on-bit (WOB) required for a particular rate-of-penetration (ROP). This paper presents the results of comparing such a model to laboratory drilling tests for four radically different bit designs in four different rocks. The geometry of each cutter on the bit was determined by detailed measurements of the bit with a 3-axis coordinate measuring machine. Drilling tests were conducted by "reaming" rock with an 8-1/2" bit that had been previously drilled with a 6-1/4" bit. Only the peripheral cutters engaged the rock during the reaming. Additional tests were conducted where the WOB and torque were recorded while drilling a pilot hole into the top of a flat rock and drilling through two different bed boundaries with constant ROP. The model predictions compared well to the measured data for both the reaming tests and the pilot hole tests.