The weight of a gallon of gasoline is approximately 6.3 pounds, according to the U.S. Department of Energy. This includes only the weight of the gasoline, not the weight of its container.
A gallon of gasoline weighs roughly 6.3 pounds, depending on the density of the gasoline. If using the metric system, the approximate mass of gasoline is 2.8 to 2.9 kilograms, depending on its density. Gasoline is approximately 87 percent carbon and 13 percent hydrogen by weight. When gasoline is burned, it produces 20 pounds of carbon dioxide. This is because the carbon molecules in gasoline, which have a molecular weight of 12, combine with two oxygen molecules in the air with a molecular weight of 16 each. The carbon combines with oxygen to create a substance almost four times as heavy as itself.