Article — Gallons to Kilograms (gal to kg) Converter
Gallons to Kilograms: Mass of a Gallon for Common Liquids
A US gallon of water weighs 3.785 kg at 4°C. A US gallon of gasoline weighs 2.86 kg, diesel weighs 3.22 kg, whole milk weighs 3.91 kg, and honey weighs 5.38 kg. To convert any liquid from gallons to kilograms, multiply the volume in gallons by 3.78541 (liters per US gallon) and by the liquid's density in kg/L. The Imperial gallon is 20 percent larger than the US gallon — an Imperial gallon of water weighs 4.546 kg.
Gallons measure volume, kilograms measure mass. The bridge between them is density, and density is different for every substance. The numbers below cover the substances people search for most: water, fuel, dairy, and industrial liquids.
Water: the 3.785 kg baseline
The weight of a US gallon of water is a derived value, not a measurement. The metric system defines one liter of water at 4°C as exactly one kilogram. A US gallon equals 3.78541 liters. Multiplying gives 3.7854 kg — the canonical answer for the most-asked question in this conversion.
Every other liquid in the calculator works the same way. Density in kg/L (which equals density in g/mL) multiplied by 3.78541 gives kg per US gallon. Gasoline is 0.755 kg/L × 3.78541 = 2.858 kg/gal. Honey is 1.42 kg/L × 3.78541 = 5.375 kg/gal. The gallon-to-liter constant does all the unit work; only the density changes between substances.
The 1 kg per liter of water relationship was set deliberately in 1795 when the metric system was designed. A committee of French scientists picked the gram and kilogram to make water — the universal reference fluid — a clean round number. They did the same for the meter, defined as one ten-millionth of the distance from the equator to the North Pole. Both definitions have been refined since, but the 1 L = 1 kg water relationship is still the practical anchor of every kilogram measurement on Earth.
Gallons to kg for fuels
Fuel is bought by volume but consumed by mass. The chemical energy released by combustion is proportional to mass, not gallons, which is why aviation, marine, and freight industries track fuel in kilograms or pounds even though they purchase it in gallons or liters.
Gasoline averages 0.745-0.760 kg/L depending on the blend, with a typical pump value of 0.755 kg/L or 2.86 kg per US gallon. Diesel sits at 0.82-0.86 kg/L or 3.22 kg/gal, about 13 percent denser than gasoline. Jet A-1 (aviation kerosene) is 0.804 kg/L or 3.04 kg/gal. Ethanol blends like E85 fall between gasoline and ethanol at 2.94 kg/gal.
- Gasoline 2.858 kg/gal (varies with summer/winter blend)
- Diesel #2 3.218 kg/gal (denser than petrol by 13 percent)
- Jet A-1 kerosene 3.043 kg/gal (used for commercial aviation)
- Ethanol 2.987 kg/gal (denser than gasoline by 4 percent)
- Liquid propane 1.93 kg/gal (lightest common fuel)
- Heating oil 3.20 kg/gal (essentially diesel #2)
Service-station pumps measure gallons at the nozzle, not kilograms at the tank. Most US states require pumps to be temperature-corrected to 60°F (15.6°C), but several southern states do not. In Texas in August, a gallon of fuel pumped from a 100°F underground tank weighs about 1 percent less than a gallon from a 60°F tank. This is the "hot gallon" problem that consumer-rights groups have raised in court multiple times since 2007.
US gallon versus Imperial gallon
Two gallons exist. The US gallon is 3.78541 L; the Imperial gallon (UK, parts of Canada and the Caribbean) is 4.54609 L. The Imperial gallon is 20 percent larger, which means everything is 20 percent heavier on the imperial side. A US gallon of water weighs 3.785 kg; an Imperial gallon of water weighs 4.546 kg.
Imperial was defined in 1824 as the volume of exactly 10 lb of water at 62°F — a round-number relationship that British metrologists liked. The US, having broken from British units in 1776, kept the older 231-cubic-inch wine gallon. A UK driver who fills a 10-gallon tank with petrol takes on 12 US gallons, or 45 liters; the fuel mass is 34.3 kg instead of the 28.6 kg of a US 10-gallon fill.
Food liquids: milk, oil, honey
Dairy has the cleanest gallon-to-kg numbers because it is heavily traded and tracked. Whole milk averages 3.91 kg per US gallon, with about 1 percent spread between dairies. Skim milk runs slightly higher at about 3.93 kg/gal because removing the lower-density milk fat raises overall density. Cream goes the other way: heavy whipping cream is 3.74 kg/gal (less than water) because of trapped air and emulsified fat.
Cooking oils cluster at 3.48-3.50 kg/gal across olive, canola, sunflower, and vegetable varieties. The differences are too small to matter outside laboratory work. Honey and syrups are the heaviest food liquids: pure honey is 5.38 kg/gal, maple syrup is 5.03 kg/gal, and high-fructose corn syrup is 4.99 kg/gal. A 55-gallon drum of honey weighs about 296 kg — half again as much as the same drum of vegetable oil at 193 kg.
Bulk-liquid freight pricing usually goes by metric tonne, not by gallon. To convert: tonnes = gallons × density (kg/L) × 0.00379. A 5,000-gallon tanker of water carries 18.9 tonnes; the same tanker of honey carries 26.9 tonnes. Always confirm density with your shipper before booking — the same trailer cannot legally carry the same volume of every liquid because of axle-weight limits.
Temperature and density correction
Density depends on temperature. Water drops about 0.4 percent in density from 4°C (peak) to 100°C (boiling). Petroleum products are more sensitive at about 0.07 percent per °C, or 7 percent across a 0-100°C range. The 2.86 kg/gal gasoline figure is correct for 15°C; gasoline at 30°C is closer to 2.83 kg/gal.
Wholesale petroleum trades through API gravity scales that automatically correct for temperature. Crude oil bought as "15 API at 60°F" has a defined density of 0.964 kg/L; deliveries are settled at that reference temperature regardless of the actual tank temperature. Retail fuel does not get this same treatment in most US states, which is the basis of the recurring "hot fuel" complaint mentioned above.
water (US gal) × 3.785 = kgwater (imp gal) × 4.546 = kggasoline (US gal) × 2.86 = kgdiesel (US gal) × 3.22 = kgmilk (US gal) × 3.91 = kghoney (US gal) × 5.38 = kgAviation and freight in kg
Aircraft fuel is loaded by volume but tracked by mass because lift capacity is set by total weight. A Boeing 737 burns about 2,840 liters (750 US gallons) of Jet A per hour, which at 0.804 kg/L is roughly 2,283 kg per hour. Dispatch sheets list fuel in kg; the pilot converts to gallons or liters only when telling the fueler how much to load.
Ocean freight rates for bulk liquids are quoted in metric tonnes, never gallons. A 6,000-gallon trailer of diesel carries about 19.3 tonnes; the same trailer of corn syrup carries 30 tonnes. US trucking weight limits are set per axle, so the same trailer cannot legally carry the same gallon load of every liquid. Honey shippers run on different routes than gasoline shippers for exactly this reason.