It depends how concentrated it is. If it is 100% pure, then it weighs 1.840 g/mL, and so 1 gallon weighs 6965.15 g, or 6.965 kg (3785.41 mL per gallon). That's equal to 15.35...
if u gathered all the sulfuric acid a car produces in a week, you could fill up 3 gallons..... Note to self: take the bus
If assuming identical volumes, pure sulfuric acid is 1.86 times heavier than water.
In concentrated sulfuric acid usually about 1%