What is the minimum takeoff fuel requirement policy for commercial aircraft?
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.