Geogrid type and aperture size of the grid openings play a significant role in the performance of mechanically stabilized pavements. In the present study, three types of biaxial geogrids were used to quantify the influence of aperture size on the corresponding benefit quantifiers. Large-scale model pavement experiments (LSMPE) were conducted to study the behavior of geogrid stabilized unbound model pavements overlying a wide range of subgrades with California bearing ratio (CBR) equal to 1%, 5%, and 7%. Pavement sections were prepared in a test chamber measuring 1.5 m (length) × 1.5 m (width) × 1.0 m (height), and the load was applied through a rigid 300-mm-diameter circular plate using a 100 kN actuator. The influence of aperture size ratio (ratio of the size of the grid opening to the nominal size of aggregate) on load-settlement behavior was studied. The optimum aperture ratio for effective interlocking and particle strike-through mechanisms was proposed by varying the ratios from 1.0 to 2.0. Lastly, the benefit factors, i.e., modulus improvement factor (MIF) and layer coefficient ratio (LCR) of geogrid stabilized pavements, were presented. LSMPE test results showed significant geogrid-aggregate interaction when the ratio of the equivalent aperture size of geogrid to aggregate particle size ranged from 1.0 to 1.63. This could be attributed to the effective interlocking of aggregates within the apertures of the geogrids. The overall MIF and LCR values ranged from 1.38 to 2.2 and 1.19 to 1.46, respectively, for the tested cases of the study. © ASCE.All right reserved.