What is the minimum takeoff fuel requirement policy for commercial aircraft? I am currently working on a fuel burn analysis of a particular route (ATL to DCA). I really want 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 have more fuel (20,000lbs) 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?
14 CFR 121.639 Requires an airliner to have enough fuel to reach the destination, then fly to the (most distant) alternate, then fly after that for 45 minutes. If you want to know exactly how much fuel that is for a particular airplane on a particular route, you have to refer to that airplane's POH and plan the flight. It will also depend on the winds aloft and what airport is chosen as the alternate.