With large piston airliners (and I have flown several, including...Lockheed 1649 Constellation, DC6/7, Boeing 377) tank capacity was always indicated in US gallons, not weight.
Fuel uplift by US gallons, fuel consumed in US gallons.
Fuel temperature effect made little difference, with these aircraft.
Jets...a whole different scenario.
Been there, done that.
Them's the facts.