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Gross vehicle weight is regulated by both state and federal law on the highways, so trucks and commercial vehicles are subject to inspection at weigh stations. A key factor for many vehicle operators in complying with such laws is calculating their fuel weight.
How much does a gallon of diesel weigh? A gallon of diesel weighs 7 pounds on average; however, this can vary because of the weather, the fuel grade, and the cetane rating of your diesel fuel.
While the differences might seem minor, this adds up quickly in large rigs with tanks that hold anywhere from 100 to 300 gallons of fuel. In this article, we will review the factors that contribute to diesel’s overall weight.
The Average Weight of Diesel Types
The three main classes of diesel are number 1 (1-D), number 2 (2-D), and number 4 (4-D) with differing viscosities and pour points. The main standard for diesel fuel oils in the United States is ASTM D975, while the European Union and many other nations go by EN 590.
#1 Diesel (1-D)
Number 1 diesel is used primarily for cold weather conditions and has a lower viscosity. It is ALSO chemically very similar to kerosene. The Engineering ToolBox reports the density of number 1 diesel at 54.6 lb/ft3 at 59°F (15°C). Converted to pounds per gallon, that comes to about 7.3 pounds per gallon—a little higher than number 2 diesel (source).
#2 Diesel (2-D)
The most common form of diesel for normal and warm weather conditions is number 2 diesel, which has a higher viscosity than number 1 diesel.
The density of 2-D diesel is reported at 53 lb/ft3 or 7.09 pounds per gallon at 59°F, but standards have been moving closer to those of the European Union EN 590 as of late in parts of the US.
In the New England and the Mid-Atlantic States, a gallon of number 2 diesel fuel now weighs between 6.96 lbs and 6.91 lbs within the room temperature range of 59°F to 76°F. At colder temperatures like 32°F, a gallon of diesel will weigh about 7.05 lbs.
Diesel expands in warm weather and at very high temperatures like 110°F, a gallon of diesel will weigh about 6.8 lbs. These numbers are based on an average density of 51.84 lb/ft3 for diesel, reported by AVCalc LLC, a company based in New Jersey (source).
The European Standards Organization (CEN) requires the density of diesel to fall within a certain range. The current standard, EN 590, was introduced in 2005.
At 59°F (15°C) the required range is 820 kg/m3 (51.19 lb/ft3) to 845 kg/m3 (52.75 lb/ft3), or an average of 51.97 lb/ft3. That converts to a range of 6.84 to 7.05 lbs per gallon or an average of 6.945 lbs (source).
#4 Diesel (4-D)
Number 4 diesel is for low-speed and medium-speed engines that run at a relatively constant speed. This includes railroad locomotives and power generators in plants. Number 4 diesel has a higher density of 59.9 lb/ft3 or 8 pounds per gallon.
Biodiesel B5 is composed of 5% biodiesel and 95% regular diesel. Not to be confused with renewable diesel or green diesel, biodiesel is regulated by the ASTM D6571 standard.
B5 is the only type of biodiesel fuel that doesn’t violate manufacturer’s warrantees, though most engines can run on blends of up to 30%. B100 or 100 percent biodiesel has a density of 7.3 pounds per gallon at 59.9°F (15.5°C) and a specific gravity of 0.88 (source).
Marine Diesel Fuel
There are marine diesel engines that operate on diesel fuel, and there used to be a separate ASTM standard for these known a D2069 before it was withdrawn. D2069 listed DMX, DMA, DMB, DMC, and residual fuels, but there are marine diesel engines that use number 2 diesel (source).
The Cetane Number
Hexadecene (C16H32) or cetane is a highly viscous alkene used in diesel, and the cetane level of diesel is closely related to its overall weight.
The minimum cetane number in Europe is much higher at CN 51 than in America, where the ASTM D975 standard requires a minimum cetane rating of only CN 40 for number 1 and number 2 diesel.
The typical cetane number found in most states is around CN 42 to CN 45, although in New England and the Mid-Atlantic states this has been raised to CN 50 by the Ozone Transport Commission. California requires that diesel have a minimum cetane rating of 53.
API Gravity and Specific Gravity
The ASTM D287 standard measures API gravity, a standard established by the American Petroleum Institute to determine the weight of petroleum relative to water. This also directly correlates with the energy level of diesel; the higher the API, the lower the energy.
The specific gravity is inversely related to API gravity, meaning that the higher the specific gravity, the higher the energy. The ASTM API limit range for number 2 diesel is 30 to 45 or a specific gravity range of 0.876 to 0.802 (source).
The specific gravity of diesel fuels can range from a low of 0.81 to a high of 0.96 at 60°F (source).
Higher Cetane Reduces Weight
The specific gravity of a liquid can be multiplied by the density of water in pounds per gallon at 60°F, which is 8.328 pounds/US gallon, to determine the weight of that liquid in pounds per gallon (source).
The agricultural supply cooperative Gromark, in Illinois, reports that standard number 2 diesel fuel usually has an API gravity between 32 and 34, which converts to a specific gravity of 0.8654 to 0.855 (source).
This produces a range of 7.21 lbs to 7.12 lbs for standard number 2 diesel.
A higher cetane number results in higher API gravity and lower density in fuel when achieved through the refining process.
High cetane fuel has a rating of 36 to 38 or a specific gravity of .8448 to .8348. In this case, the higher cetane number actually means fewer BTUs, less horsepower, and less fuel economy. It does, however, produce a lower weight range of 7.04 lbs to 6.95 lbs.
Is a Canadian Gallon Heavier than a US Gallon?
While a number of websites report that a Canadian gallon is greater than a US gallon, Canada began to move away from the Imperial system of measurement to the metric system in 1970.
Instead of measuring fuel in gallons, they have fuel listed in liters. There are about 3.78 liters to a US gallon, and 1 liter of diesel weighs about 1.83 lbs.
There were Canadians who resisted the conversion to the metric system and still used the Imperial gallon for many years after.
A US gallon is smaller than an Imperial gallon, which has caused a great deal of confusion along the border. A US gallon would only make up 0.86 Imperial gallons, and an Imperial gallon would make about 1.20 US gallons.
It’s still possible that you might run across a gas station in Canada that lists prices in gallons, but it will be hard to know offhand if they’re referring to Imperial gallons or US gallons. It would make sense for a business-savvy station along the US-Canada border to list prices per US gallon.
If you’re not careful, though, you could be taking on more weight than you intended if they’re using Imperial gallons. The weight of an Imperial gallon of diesel with an average density of 51.84 lb/ft3 would be 8.29 lbs. At 100 gallons, that could be a difference of 133 lbs!
Just because the prices are higher in Canada doesn’t mean you’re getting more fuel either. Taxes on fuel are much higher in Canada than in the United States.
Fuel standards in Canada are determined by the Middle Distillates Committee of the Canadian General Standards Board. These tend to favor the European EN 590 standard and the higher cetane number.
With a higher cetane number, the weight of a US gallon of Canadian diesel will probably weigh less than a US gallon of standard number 2 diesel with a cetane rating of 42-45.
What do 100 Gallons of Diesel Weigh?
The most common rule of thumb for truck drivers is to estimate their fuel weight at 7 lbs per gallon. For example, a tank carrying 100 gallons of fuel would contribute about 700 lbs to the truck’s overall weight.
The number would be fairly accurate for number 2 diesel, but number 1 diesel at 7.3 lbs per gallon would be closer to 730 lbs. That extra 30 lbs could be the difference that determines whether or not you get a ticket.
Weight Limits & Fuel Capacity
Since 1974, Federal weight limits have included a gross vehicle weight of 80,000 lbs, a single-axle weight of 20,000 lbs, and a tandem axle weight of 35,000 lbs (source). Depending on the state, any vehicle weighing over 10,000 lbs may have to go through weigh stations.
Class 3 & 4
While you do not have to have a CDL to operate anything under a class 5 truck, these vehicles do weigh over 10,000 lbs and may be required to check-in at weigh stations.
Class 4 trucks can weigh between 14,001 and 16,000 lbs, and these box trucks are commonly used as delivery trucks (source). With a fuel capacity range of 20 to 40 gallons, you’re looking at a typical fuel weight when full of 140 to 280 lbs.
Class 5-7 Trucks
Class 5 trucks have 2 axles and 6 tires, a class 6 truck has 3 axles, and a class 7 can have 4 or more axles. They have a gross vehicle weight rating (GVWR) range of 16,001 to 19,500 lbs, 19,501 to 26,000 lbs, and 26,001 to 33,000 lbs respectively.
Typical fuel tank sizes include 45 gallons, 75 gallons, and options that include a dual fuel tank combined capacity of 115 gallons.
In most states, busses are not required to go through weigh stations. But in some states, like Pennsylvania and California, they do (source).
A coach is a type of bus used for intercity transportation, while transit buses tend to be regional or intra-city. The most well-known example in the US is the Greyhound bus. Greyhounds have a fuel capacity ranging from 185 to 220 gallons.
Ninety-four percent of school busses use diesel, and a school bus can carry between 60 and 100 gallons of fuel (source).
School bus weight limits vary by type. Type A1 is less than 10,000 lbs while A2 can be over 10,000 lbs. Types B and C are over 10,000 lbs with most Type C buses between 23,500 and 29,500 lbs. Lastly, type D buses are between 25,000 and 36,000 lbs (source).
Class 8 Trucks
Supply chains throughout the country—especially in the wholesale, manufacturing, and construction sectors of the economy—rely heavily on tractor-trailer truck drivers (source).
Class 8 trucks are above 33,000 lbs, and they are the most common vehicles used for commercial trucking. Class 8 diesel trucks usually carry saddle tanks, which are two fuel tanks mounted on either side of the truck for balance.
The most common loadout for a long-haul truck is two 125 gallon tanks for a total fuel capacity of 250 gallons. Some trucks have two 150 gallons tanks for a total of 300 gallons and, although rarer, some trucks can carry over 300 gallons.
A long-haul truck with a 250-gallon capacity could be carrying as much as 1,750 lbs of fuel to 1,825 lbs. With a capacity of 300 gallons, that would be 2,100 lbs to 2,190 lbs.
Truckers like to have about 31,000 lbs on their drive axle to give them 3,000 lbs to spare. That’s more than enough for rigs with tanks that hold under 300 gallons.
The most common setup is 12,000 lbs on the steering axle and 34,000 lbs on two separate tandem axles for a total overall weight of 80,000 lbs.
On the classic trucks with a sloping nose, the fuel tanks are shifted more toward the steering axle under the cab doors and will distribute their weight there. On long-hood trucks, the tanks are further back and the weight will tend to be more on the drive axles.
Sulfur has a comparatively high specific gravity at 68°F (20°C) between 2.07 and 1.97, meaning that the lower sulfur levels also contribute to the decreasing weight of diesel.
Both number 1 and number 2 diesel come in S15, S500, and S5000 variants with the number representing the sulfur level in parts per million (ppm). As environmental concerns have grown, the higher-sulfur variants are being phased out.
Number 2 S500 low-sulfur diesel was in use on highways before 2006. S500 continued to be used off-road until 2014. After 2014, Number 2 S15 ultra-low sulfur diesel (ULSD) became the standard (source).
Red and Green Diesel
Red diesel is intended for off-road use, mainly in tractors, off-road equipment, or as home-heating oil. Red diesel is dyed red in order to distinguish it from regular diesel since red diesel is not legal on the road and is not taxed like regular diesel.
Green diesel or renewable diesel is “green” in the sense that it is clean, renewable, and environmentally friendly. Green diesel is produced from non-fossil resources and its chemical structure differs from methyl-ester biodiesel (source).
Green diesel has very little sulfur and has an even higher cetane level than ultra-low sulfur diesel (source). Honeywell International, with its headquarters in North Carolina, boasts that its green diesel has a cetane rating between 75 and 90 and sulfur level less than 2 ppm (source).
Natural Gas Alternatives
The price of natural gas is much lower than that of oil-based gases, and companies like Shell are interested in the possibility of converting natural gas into diesel to make healthy profits (source).
While gas-to-liquids plants are expensive to build, access to an adequate supply of natural gas can make the investment more attractive.
The largest gas-to-liquid plant is owned by Shell and Qatar Petroleum. Pearl GTL is projected to produce the equivalent of 3 billion barrels of oil over its lifespan from the North Field of the Arabian Gulf (source).
Other companies are experimenting with using compressed natural gas (CNG) and liquid natural gas (LNG) as replacements for diesel fuel. Currently, these alternatives are still not as fuel-efficient as diesel with a gallon of diesel producing the same energy as 1.7 gallons of LNG (source).
Compressed natural gas (CNG) and liquefied natural gas (LNG) are used in specialized natural gas vehicles or NGVs. Over 130,000 NGVs are on the road today (source).
Compressed natural gas is lighter than air, being composed of high levels of methane. Liquefied natural gas is cooled to liquid form in order to reduce its volume and increase the amount of fuel a vehicle can hold. As a result, LNG fuel is preferred for heavy-duty NGV trucking.
As the requirements for diesel are being raised due to environmental concerns, the weight of diesel per gallon has decreased to a little less than 7 lbs at 6.94 lbs. In areas that still use a lower cetane rating or have higher levels of sulfur, diesel will weigh a little more at 7.09 to 7.30 lbs per gallon.
The common rule of thumb for truck drivers of calculating fuel weight at 7 pounds per gallon still holds true for the most part. In colder weather conditions, it would be wise to calculate the weight as a little over 7 lbs per gallon, especially if the diesel you’re using has a cetane number below 50.