Subgrade reaction modulus (Ks) is one of the most important soil parameters to perform structural calculations and analysis. Ks directly affects the determination of dimensions and reinforcement of foundations. Therefore, its exact and accurate determination is of significant importance in terms of economy and safety, especially in large structures. To calculate the coefficient, it is possible to use either the previously presented experimental relations or directly from field tests such as plate load tests. In the present study, 36 plate load tests (PLTs) were performed on the rigid plates with 20 cm, 30 cm and 45 cm diameters (12 tests  on each plate) on coarse-grained sediments of the west of Mashhad, Iran. Then the results were analyzed and a new equation was presented to determine Ks by considering soil and foundation properties no need to costly tests. Then, a new model was presented to generalize the results of plate load tests to actual dimensions of the foundation in the case of the test because of the difference between real foundation dimensions and loading tests plates. Also,  the obtained equation and model were validated and results were compared with previous relations and tests outputs.