There are US gallons and Imperial gallons
Imperial gallons are bigger =10 pounds of distilled water at standard temperature and pressure.
US gallons = 8.32673133 pounds water at s.t.p.
One once
100 US gallons of water is about 835 pounds.
834.5 pounds.
2 liters
150 milliliters of pure water weigh 150 grams.
At 17oC one gallon of water weighs 4.536kg.
One cubic centimeter of water would fit into that cup, and it would weigh 1 gram.
I litre of water weighs one kilogram on year and would weigh 0.1 kilograms.
about 4kg
One gallon of water weighs about 8.35 pounds (about 3.8 kilograms).
About 8.35 pounds.
That would depend on the buoyancy of the feathers.