Article — Gallons to Grams Converter
Gallons to grams: water, milk, honey, oil, and fuel weights
A US gallon of water weighs 3785.41 grams at 4 degrees C. To convert any gallon volume to mass in grams, multiply by 3785.41 (for US gallons) and then by the substance specific gravity. Honey is 1.42 times denser than water, so a gallon weighs 5375 g; gasoline is 0.72 times the density, so a gallon weighs 2726 g.
Gallons measure volume; grams measure mass. The two cannot be converted directly without knowing the density of the liquid involved. The same gallon container holds different masses of water, oil, honey, and gasoline because each liquid packs different numbers of molecules into the same volume. This converter handles the eight most common liquids that show up in cooking, food service, fuel handling, and chemistry.
What is gallons to grams conversion?
Gallons to grams conversion translates a volume in US gallons into a mass in grams, accounting for the density of the specific liquid. The US gallon is defined as 3.785411784 liters, which equals 3785.41 milliliters. One milliliter of water at 4 degrees Celsius weighs exactly 1 gram by definition, so a gallon of water weighs 3785.41 g.
For any other liquid, multiply the volume by the substance specific gravity (its density relative to water). Milk has SG 1.03, so a gallon weighs 3899 g. Olive oil has SG 0.915, so a gallon weighs 3464 g. The calculation is the same formula regardless of substance: gallons times 3785.41 times specific gravity.
The gallons to grams formula
The conversion uses three constants and one variable. The gallon definition (3785.41 mL) is exact. The water density (1.000 g/mL at 4 degrees C) is exact by definition. The specific gravity of the substance is the variable, looked up from a density table. Multiply them together and the answer is mass in grams.
grams = gallons * 3785.41 * SG gallons = grams / (3785.41 * SG)1 US gal water = 3785.41 g 1 imp gal water = 4546.09 gSG honey = 1.42 SG gasoline = 0.72For mental math, treat water as 3800 g/gal. Then scale: honey is roughly 1.4 times water (5300 g/gal), oil is 0.92 times (3500 g/gal), gasoline is 0.72 times (2700 g/gal). The shortcuts are within 1% of the exact values and good enough for any field estimate.
How many grams in a gallon of water
The water answer is a definition stacked on a definition. The US gallon is exactly 231 cubic inches, which works out to 3785.411784 milliliters using the exact 25.4 mm per inch ratio. Water at 4 degrees Celsius has a density of exactly 1.000 g/mL — this was the original definition of the gram, set by the French Academy in 1795. Multiplying gives 3785.41 grams.
At room temperature (20 degrees C / 68 degrees F), water density drops to 0.9982 g/mL, so a gallon weighs 3777.6 g. The 0.2 percent difference is below the precision of most kitchen scales and is ignored in everyday work. Engineering and laboratory references usually state 3785 g/gal as the standard.
The number 3785.41 mL per gallon comes from a defined chain: the US gallon was the British Queen Anne wine gallon (231 cubic inches), and 1 inch is exactly 25.4 mm. Cubing the inch-to-mm factor and multiplying by 231 gives 3785.411784 mL to the millionth of a milliliter. The whole conversion chain reduces to exact arithmetic.
Gallons to grams for milk, honey, and oils
Whole milk weighs 3899 g per US gallon, slightly more than water because of dissolved proteins, lactose, and minerals. Skim milk is heavier still (3917 g/gal) because removing the fat increases overall density. Cream and half-and-half are lighter than whole milk; heavy cream runs around 3700 g/gal.
Honey is the heaviest common food liquid at 5375 g per US gallon, about 42% denser than water. The exact value depends on water content: 5300 to 5450 g/gal is the commercial range. Crystallized honey is slightly denser than liquid honey because the crystals pack tighter. Maple syrup runs 5034 g/gal, corn syrup 5224 g/gal, and molasses 5375 g/gal.
Cooking oils are lighter than water. Olive oil weighs 3464 g per US gallon, vegetable oil 3483 g, and coconut oil 3502 g. The lighter density is why oils float on water and why they spread in thin films across surfaces. Industrial lubricating oils run heavier (0.88 to 0.92 g/mL) but stay below water density.
Gallons to grams for gasoline, diesel, and ethanol
Pump gasoline weighs 2726 g per US gallon (density 0.72 g/mL at 60 F), making it the lightest common liquid in this calculator. Diesel is denser at 3218 g/gal (0.85 g/mL). Jet A jet fuel sits between them at 3066 g/gal. Ethanol-only fuel runs 2987 g/gal. E10 gasoline (10% ethanol) weighs about 2752 g/gal because the ethanol blend is slightly denser.
Fuel weight matters in aviation and freight pricing. A truck carrying 8000 gallons of gasoline hauls 21.8 metric tonnes; the same truck with diesel hauls 25.7 tonnes. Tank cars and pipelines bill by volume, but DOT weight limits cap the actual amount of fuel a truck can carry, so denser products mean fewer gallons per shipment.
The Imperial gallon (UK, Canada, some Caribbean) is 20% larger than the US gallon. A recipe calling for one gallon of milk weighs 3899 g if US or 4682 g if Imperial — different enough to ruin a batch. American recipes, fuel pumps, and density tables all default to US gallons unless explicitly noted otherwise.
US gallon vs Imperial gallon
The two gallons have separate histories. The US gallon descends from the British wine gallon (1707) of 231 cubic inches. The Imperial gallon was redefined in 1824 as the volume of 10 pounds of water at 62 degrees F, which works out to 4546.09 mL. The Imperial gallon is exactly 1.20095 times larger than the US gallon.
Confusing the two is the single most common gallon-to-grams mistake. A British baker following an American recipe doubles a discrepancy that propagates through every measured liquid in the recipe. Always confirm the gallon convention before converting, especially for cross-Atlantic recipes and historical engineering references.
Temperature and density effects
Density changes with temperature for every liquid. Water shifts 0.2% between 4 degrees C (1.000 g/mL) and 20 degrees C (0.998 g/mL). Cooking oils shift more, around 0.5 to 0.7 percent across the same range. Fuels are the most sensitive: gasoline can shift 1% between summer and winter blends because the underlying composition also varies.
Commercial fuel sales apply temperature compensation. Pumps measure the mass of fuel rather than just the volume, correcting to a reference temperature of 60 F. Without correction, customers buying gasoline on a hot day would receive less mass per gallon than customers buying on a cold day, even though both pay the same per-gallon price.
If your substance is not in the list, look up its density in g/mL and multiply by 3785.41 to get g per US gallon. Engineering Toolbox and USDA FoodData Central publish densities for hundreds of common liquids. For homemade calibration, weigh exactly 100 mL of the substance and divide the gram reading by 100.
Quick reference values
Per US gallon, the eight substances in this calculator cover the everyday range from gasoline (lightest) to honey (heaviest).
- Water = 3785 g/gal (SG 1.00)
- Milk (whole) = 3899 g/gal (SG 1.03)
- Honey = 5375 g/gal (SG 1.42)
- Olive oil = 3464 g/gal (SG 0.915)
- Vegetable oil = 3483 g/gal (SG 0.92)
- Gasoline = 2726 g/gal (SG 0.72)
- Diesel = 3218 g/gal (SG 0.85)
- Ethanol = 2987 g/gal (SG 0.789)
- Imperial gallon water = 4546 g/gal (20% larger volume)
- Reverse rule: 1000 g water = 0.264 US gal = 0.220 Imperial gal