128 Ounces To Gallons. 128 oz to g conversion. V(gal) = 5(fl oz) × 0.00781 = 0.03905gal. A gram is a unit of weight equal. 128 ounce = 1 gallon. Web a gallon is 128 ounces, which means four 32 oz. Web that way you won’t have to figure out how to measure odd fractions …