A series of large-scale model experiments were carried out on different geogrid- and geocell-reinforced base courses to evaluate realistic base-layer coefficients to design flexible pavements. The placement depth of reinforcement was first determined under monotonic loading on designed unreinforced pavement sections over a very weak subgrade (resilient modulus of 10 MPa) prepared in a 2.25-m3 size test chamber. A structural support offered by the reinforcement alone in the base layer was quantified through the modulus improvement factor (MIF) for varying subgrade conditions. The MIF values ranged between 1.5 and 3.5 for geogrid-reinforced bases and 1.4 and 5.0 for geocell-reinforced base layers placed over different subgrade conditions. Further, a range of laboratory-produced MIF values and semiempirical mechanistic design principles were used to analyze the flexible pavements to get the base-layer coefficients for various geogrid- and geocell-reinforced pavements. In this analysis, the traffic was considered from 2 million to 150 million equivalent single-axle loads, subgrade resilient modulus (Mrs) from 10 to 85 MPa [corresponding a California bearing ratio (CBR) from 1% to 8%], and MIF from 1.2 to 3.5 for geogrids and 1.2 to 5.0 for geocells. A new set of apt base-layer coefficients for geogrid- and geocell-supported base layers was developed through a systematic analysis. The layer coefficients for geogrid-reinforced bases ranged from 0.15 to 0.35 and 0.175 to 0.425 for geocell-reinforced base layers. The proposed models were validated with an as-built pavement section from Montana state and the available design approaches. The proposed design approach has reduced the thickness of a geogrid-reinforced base layer by about 40%, and it is 50% for the geocell-reinforced base layer. © 2022 American Society of Civil Engineers.