Minimum fuel requirement before takeoff

Hi! I am currently working on fuel burn analysis of the particular route. (ATL to DCA) I have really wanted to predict takeoff weight of the flight; however, I realized that it’s not easy to get the information. Instead, I may want to gather information about minimum fuel requirement for the flight. For example, I heard from the pilot of the flight that they should hold fuel (20,000lbs) more than the minimum fuel (15,000lbs) before takeoff. Could anyone please let me know where I can get this information such as minimum fuel requirement for A320 from ATL to DCA?