Desalination of salt water is becoming a major industrial activity across the globe. The industry provides a sustainable source of fresh water for various urban and industrial applications. In this regard, the multistage flash desalination (MSF) process represents more than 56% of the world desalination market. This process was introduced in the late 1950s and since has proved to be highly reliable and provided high production capacity units. Recently, there has been renewed interest in the MSF industry, especially in the Middle East countries. The focus of this study is to develop a number of design correlations of the MSF flashing stage. These correlations include discharge coefficient (Cd), non-equilibrium allowance (NEA), and overall heat transfer coefficient (U). This development is the first of its kind in the open literature, since it is based on a large database that includes the test data from six large-scale MSF units located in different stations in the Gulf States. The database was collected during steady-state operation. The correlations for the Cd and the NEA were developed for two different types of inter-stage devices. Also, the U correlation was obtained for both the heat gain and heat rejection sections. The developed correlations show good agreement with available literature correlations. This study provides the literature with valuable design correlations, based on data collected from existing MSF plants.