Final reserve fuel is 30 minutes.
(as per EASA IR-OPS AMC1 CAT.OP.MPA.150(b) (5) (ii) - Fuel policy: "for aeroplanes with turbine engines, fuel to fly for 30 minutes at holding speed at 1500ft (450m) above aerodrome elevation in standard conditions, calculated with the estimated mass on arrival at the destination alternate aerodrome or the destination aerodrome, when no destination alternate aerodrome is required.")
This is approximately 3.1 tons for a B773 and 2.6 tons for a B772.