How Many Grams are in One Gallon?

When converting grams to gallons, you first need to know what the density of what you are measuring is. Grams are units of mass while gallons are units of volume. A liter of water weighs one kilogram, or one thousand grams, and a gallon is 3.78 liters, so a gallon of water would weigh around 3780 grams.
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