As many regions around the world are facing water scarcity, reverse osmosis (RO) has attracted attention to supply fresh water to such areas. To design and develop energy-efficient RO processes, accurate osmotic pressure values of salt water are critical, yet conventional models of osmotic pressure have significant deviations from the actual values. In addition, absence or high charge of authentic osmotic pressure databases prevents accessing authentic data. Here, we propose combining the Chang correction factor, a polynomial in solution concentration, with traditional osmotic pressure models to approximate the osmotic pressure of dilute to concentrated solutions with high accuracy. The Chang correction factor is determined by regressing a handful of authentic osmotic pressure data divided by theoretical values calculated using traditional models. Multiplication of resulting polynomials back to corresponding traditional models enables accurate approximation of the authentic osmotic pressure of dilute to concentrated solutions with R2 approaching 1. In addition, generality of the strategy over aqueous and organic solutions is demonstrated by approximating osmotic pressure of NaCl and sucrose aqueous solutions and C2H4Cl2-C6H6 and C3H6Br2-C2H4Br2 organic solutions. The approximation strategy proposed and assessed here will be useful to simulate and develop processes for seawater desalination and various industries with high importance.