Salinity of soil and water is the most important agricultural hazard in arid and semi-arid regions. In saline soils, yield production directly influences by soluble salts in the root zone as well as by shallow water table depth. The first step for reclamation of such soils is reducing salinity to optimum level by leaching. The objective of this study was to develop a practical model to estimate water requirement for reclamation of saline-sodic soils at large scale based on some obtainable soil physical characteristics. Consequently, a large area of 3,216 ha with S4A3 salinity/sodicity class (extreme salinity and sodicity) was selected to obtain the required data. Several mathematical models were applied to the collected data to verify their estimation capability. The results indicated that at large scale, the proposed logarithmic model can provide much better estimates for leaching process than the previously proposed models.