A single US gallon of diesel fuel weighs approximately 6.9 pounds under standard conditions. This petroleum distillate is denser than gasoline because it is composed of longer hydrocarbon chains. Diesel is the preferred fuel for compression-ignition engines in heavy-duty vehicles and machinery. The weight of the fuel reflects the energy contained within that volume, which impacts logistics and engine performance.
The Standard Weight of Diesel
The industry standard for measuring diesel fuel weight in the United States is established at 60 degrees Fahrenheit (15.6 degrees Celsius). At this reference temperature, a US gallon of ultra-low sulfur diesel typically weighs between 6.9 and 7.1 pounds.
The weight is fundamentally determined by the fuel’s density, which is defined as its mass per unit volume. Diesel’s density is often expressed as Specific Gravity, comparing the fuel’s density to that of water. Since diesel is lighter than water, its specific gravity is less than 1.0, generally falling between 0.82 and 0.88.
Variables That Change Diesel’s Weight
The weight of a gallon of diesel is not a fixed constant because the fuel is susceptible to physical changes from its environment and composition. The primary cause of weight fluctuation is temperature, which causes the fuel to undergo thermal expansion. As the temperature increases, the fuel molecules spread further apart, increasing the volume while the total mass remains unchanged.
This means a gallon of warmer diesel is measurably lighter than a gallon of colder diesel. For example, a gallon measured at 106°F might weigh about 6.8 pounds, whereas the same gallon cooled to 16°F could weigh closer to 7.1 pounds. Fuel grade also introduces variability. Standard highway Diesel #2 is denser and heavier than Diesel #1, which is often used in winter blends to improve cold-weather flow. Blending in the lighter Diesel #1 reduces the overall density, causing the winterized fuel to weigh slightly less per gallon.
Why Knowing Diesel Weight Matters
Understanding the weight of a gallon of diesel has significant commercial and logistical consequences. In commercial transactions, fuel is sold by volume (gallons), but the actual energy content delivered depends on the mass of the fuel. Because temperature causes density to fluctuate, bulk fuel transfers are corrected using specialized tables to standardize the volume to the 60°F reference point.
The weight is also an important factor for transportation logistics, particularly for large commercial trucks that must adhere to strict federal and state weight limits. Fleet managers use the 7-pound-per-gallon average to calculate the gross vehicle weight. This ensures they remain below legal limits, such as the federal 80,000-pound maximum. Knowing the precise weight helps optimize payload capacity and avoid costly fines for overweight loads. The higher density of diesel provides an advantage in fuel efficiency, as more energy is packed into each gallon.