A standard U.S. gallon of #2 diesel fuel weighs approximately 7 pounds (6.9 to 7.1 lbs depending on temperature).
If you drive a truck or plan loads, you need this number fast. So, how much does a gallon of diesel weigh in real life? Seven pounds is the safe number to use for math on the road.
Fuel weight matters because every pound counts toward your limit. The U.S. Department of Transportation (DOT) enforces an 80,000 pound gross weight limit at weigh stations. Fuel is part of that total, so a full tank leaves less room for freight.
Here is a quick example. A 100 gallon tank holds about 700 pounds of diesel. Dual 150 gallon tanks hold about 2,100 pounds when full.
Warm fuel weighs a little less per gallon, and cold fuel weighs a little more. The swing is small, but it can add up across big tanks. Use 7 pounds per gallon for planning, then check your actual weight at the scale.
Types of Diesel and Their Exact Weights
Does the Type of Diesel Change the Weight?
Yes, but only by a small amount. Most trucks run on #2 diesel, so 7 pounds per gallon works for nearly every trip. Here is how the main types compare.
- #2 Diesel (standard highway diesel): About 7.0 pounds per gallon. This is the fuel at most truck stops, so use this number for your weight math.
- #1 Diesel (winter or kerosene blend): About 6.8 pounds per gallon. It is thinner and lighter, so it flows better in freezing weather.
- Red Diesel (off-road): Exactly the same as #2, about 7.0 pounds per gallon. The red dye adds no weight you could ever measure.
- Biodiesel (B5 and B20): About 7.0 to 7.1 pounds per gallon. It is slightly heavier than plain #2, but the gap is tiny.
Why is #1 diesel lighter? In cold weather, fuel suppliers blend in kerosene so the fuel does not turn thick or gel. Kerosene is a lighter fuel, so the blend weighs less. The gap is about 0.2 pounds per gallon. On a 150 gallon tank, that is roughly 30 pounds.
Red diesel is the same fuel as clear #2 with dye added. The dye shows inspectors that the fuel is for off-road use only. Farmers, builders, and heavy machinery operators can use 7 pounds per gallon for red diesel. Just remember that red diesel is not legal for highway trucks.
Biodiesel is made from plants or animal fats and mixed into regular diesel. B5 means 5 percent biodiesel. B20 means 20 percent. Pure biodiesel is a bit denser, so a blend adds only about 0.05 to 0.1 pounds per gallon. That is 5 to 10 pounds on a 100 gallon tank, which is too small to matter for most weight math.
Here is what 100 gallons weighs in each case. #2 diesel is about 700 pounds. #1 diesel is about 680 pounds. Red diesel is about 700 pounds. B20 is about 705 to 710 pounds.
The bottom line is simple. Use 7 pounds per gallon for #2, red diesel, and most biodiesel blends. Drop to 6.8 pounds only if you run straight #1 in winter. When you are close to your limit, a certified scale gives the final answer.
Standard Truck Fuel Tank Weight Conversions
Diesel Weight Chart for Standard Fuel Tanks
Use this chart when you plan a load or fill up. Every number uses 7 pounds per gallon.
| Gallons of Diesel | Weight in Pounds |
| 50 gallons | 350 lbs |
| 100 gallons | 700 lbs |
| 150 gallons | 1,050 lbs |
| 200 gallons | 1,400 lbs |
| 250 gallons | 1,750 lbs |
| 300 gallons | 2,100 lbs |
The weight of 100 gallons of diesel is about 700 pounds. That is a handy number to remember. Need another size? Multiply your gallons by 7 and you have your answer.
Most semi trucks carry dual 150 gallon tanks. That makes 300 gallons in total. A full set holds about 2,100 pounds of fuel.
Here is what that looks like at the pump. You pull in with both tanks close to empty. You fill them to the top. Just like that, you added over 2,000 pounds to your rig. That is a full ton of weight that counts against your 80,000 pound limit.
Many drivers ask what a full tank does to the steer axle. The answer depends on your truck. Tank weight is shared between the steer and drive axles, and the split changes with tank size and placement. A certified scale shows your exact axle weights.
Here are a few common setups. Dual 100 gallon tanks hold 200 gallons, or about 1,400 pounds. A 150 gallon tank paired with a 100 gallon tank holds 250 gallons, or about 1,750 pounds. Dual 150 gallon tanks sit at the top of the chart at 2,100 pounds.
Cold weather adds a small bump. Cold diesel is denser, so each gallon weighs a little more than 7 pounds. The gain is small, but it matters when you are close to your limit.
Want to save weight? Fill only what your route needs. If your next stop is 400 miles away, a full 300 gallons may be more than you need. Plan your fuel stops around your load, and you can sometimes carry more freight.
Here is the simple formula: gallons times 7 equals pounds. For 175 gallons, that is 175 times 7, or 1,225 pounds. Use it any time your tank is only partly full.
Fuel is also a moving number. Every mile you drive burns fuel and drops your weight. A truck that fuels up right before a scale will read heavier than the same truck a few hundred miles later. Weigh right after fueling if you want the heaviest reading.
Weigh Stations, Payload Capacities, and DEF
How Fuel and DEF Weight Affects Truck Load Capacity
The federal limit for a loaded semi is 80,000 pounds of gross vehicle weight. That number covers the truck, the trailer, the freight, the driver, and every fluid on board. Fuel and DEF count too. The U.S. Department of Transportation (DOT) sets this limit, and weigh stations check it.
Semi truck fuel tank weight works like freight you cannot sell. Every pound of fuel takes a pound away from your payload. A full set of dual 150 gallon tanks holds 300 gallons. At 7 pounds per gallon, that is 2,100 pounds.
Here is the math. Start with 80,000 pounds. Subtract the empty weight of your truck and trailer. Say that comes to 35,000 pounds.
That leaves 45,000 pounds for fuel and freight. Take out 2,100 pounds of fuel, and you have 42,900 pounds left for cargo. Run half tanks instead, and you free up 1,050 pounds for more freight.
Steer Axle and Drive Axle Limits
The 80,000 pound total is not the only limit. Each axle group has its own cap too. Federal rules allow 20,000 pounds on a single axle and 34,000 pounds on a tandem axle group. Most steer axles carry around 12,000 pounds, though your axle and tire ratings set the real cap.
Fuel tanks usually hang between the steer and drive axles. Most of the fuel weight lands on the drive axles, but some reaches the steer axle. The split depends on tank size and position. You can sit under 80,000 pounds in total and still be overweight on one axle.
Fill up, then weigh on a certified scale. Slide your fifth wheel forward or back to move weight between the steer and drive axles until each one is legal.
DEF Weight Per Gallon
Modern diesel trucks also carry Diesel Exhaust Fluid, or DEF. It cleans up exhaust, and many trucks lose power without it. DEF weight per gallon is about 9 pounds. That makes it heavier than diesel at 7 pounds per gallon.
DEF is mostly water mixed with urea, and water alone weighs 8.34 pounds per gallon. A 20 gallon DEF tank adds about 180 pounds when full. That is more than 25 gallons of diesel.
Cold weather barely changes DEF weight. It freezes at around 12°F, but frozen or not, plan with 9 pounds per gallon.
Now add it up. Dual 150 gallon tanks hold 2,100 pounds of diesel. A full DEF tank adds 180 pounds. Together, that is 2,280 pounds of fluid riding on your truck.
Using the same example, 42,900 pounds of cargo drops to 42,720 pounds once the 180 pounds of DEF is counted.
Use these quick formulas when you plan a load:
- Diesel gallons times 7 equals pounds of fuel.
- DEF gallons times 9 equals pounds of DEF.
- Fuel plus DEF is the weight you subtract from your payload.
For more on diesel fuel standards and properties, see the U.S. Energy Information Administration. The EPA also covers DEF standards for diesel engines.
The Impact of Temperature
Does Diesel Weigh More in the Winter?
Yes, but only by a tiny amount. Cold diesel weighs slightly more per gallon, and hot diesel weighs slightly less. The change is measured in fractions of a pound.
Most liquids grow a little when they heat up and shrink a little when they cool down. The tiny particles inside spread apart in the heat and pack closer in the cold. Scientists call this thermal expansion and contraction.
When diesel is cold, it takes up less space. More fuel fits into every gallon, so each gallon is denser and a bit heavier. When diesel is hot, it expands. Less fuel fits into a gallon, so each gallon is a bit lighter.
Here is the part many drivers miss. The total mass of the fuel never changes. Ten pounds of diesel is still ten pounds at 20°F or at 100°F. Only the space it fills changes, and a gallon is a measure of space.
Now the numbers. Diesel changes about 1 percent in size for every 20 to 25 degrees Fahrenheit. The standard 7 pounds per gallon is based on 60°F. On a 20°F morning, a gallon may weigh about 7.1 pounds. On a 100°F day, it may weigh about 6.9 pounds.
Here is what that means for big tanks. Dual 150 gallon tanks hold about 2,130 pounds of cold fuel and about 2,070 pounds of hot fuel. That gap is roughly 60 pounds between a freezing morning and a scorching afternoon.
For normal driving, do not overthink this. Use 7 pounds per gallon and move on. A swing of a few pounds will not decide whether you pass a scale. Winter fuel blends often include lighter #1 diesel, which can cancel out some of the cold weather gain.
Fleet managers should think differently. Across 200 trucks, a 60 pound swing adds up to 12,000 pounds of fuel weight that moves with the seasons. Fleets that track weight per load or payload data can use temperature to explain small gaps in their numbers.
Bottom line: use 7 pounds per gallon on the road, and save the temperature adjustments for the spreadsheet.
Diesel vs Gasoline vs Water
Diesel vs. Gasoline vs. Water: Which is Heaviest?
Water is the heaviest of the three liquids. Diesel comes second, and gasoline is the lightest. Here is the diesel vs gasoline weight comparison, with water added as a baseline.
| Liquid | Weight per U.S. Gallon |
| Water | 8.34 lbs |
| Diesel (#2) | 7.0 lbs |
| Gasoline | 6.0 lbs |
Gasoline can run from 6.0 to 6.3 pounds per gallon, so 6 pounds works for quick math. Diesel is about 1 pound heavier per gallon. That gap looks small, but it grows with tank size.
A 100 gallon tank of diesel weighs about 700 pounds. The same tank of gasoline weighs about 600 pounds. That is a 100 pound difference before you load a single box.
RV owners feel this too. A gas motorhome with a 75 gallon tank carries about 450 pounds of fuel. A diesel pusher with the same size tank carries about 525 pounds. Check your cargo capacity rating before you fill up.
Why Water in a Diesel Tank Causes Damage
Many people believe diesel sinks in water. It does not. Water weighs 8.34 pounds per gallon, so it is heavier than diesel. Diesel floats on top, and water sinks to the bottom.
That matters inside your tank. The fuel pickup sits near the bottom, right where the water collects. The pump pulls that water into your fuel lines before it reaches the clean diesel above.
Water in the fuel can ruin injectors, damage the fuel pump, cause rust, and stall your engine. Those repairs cost thousands of dollars, and a breakdown costs you a load.
Water usually gets in through condensation, a worn cap seal, or dirty fuel at the pump. Half empty tanks in cold weather build the most condensation.
Protect your rig with a few habits:
- Drain your fuel water separator on a regular schedule.
- Keep tanks fuller in cold weather to cut condensation.
- Change fuel filters on time.
- Buy fuel from busy, trusted stops.
Small amounts of water will not change your weight much. A full 100 gallons of water would weigh 834 pounds, which is 134 pounds more than the same amount of diesel. The real cost is engine damage, not scale weight.
Bottom line: diesel is heavier than gasoline and lighter than water. Use 7, 6, and 8.34 pounds per gallon, and keep water out of your tank.
Frequently Asked Questions
How much does a 5-gallon jug of diesel weigh?
A 5-gallon jug of diesel weighs about 35 pounds. That comes from 5 gallons times 7 pounds per gallon. The empty plastic jug adds a little more, usually 1 to 2 pounds, so expect a total near 37 pounds.
Metal safety cans weigh more than plastic ones. A steel 5-gallon can may add 8 to 10 pounds on its own. If you carry spare fuel on a service truck, a work trailer, or an RV, add the container weight to your load math.
Lift with your legs when you move a full jug. Thirty-five pounds feels light for a moment, then your back reminds you otherwise.
Does red diesel weigh less?
No. Red diesel weight is the same as regular #2 diesel, about 7 pounds per gallon. The red color is only a dye. It marks the fuel as tax exempt and for off-road use, and the dye adds nothing you could measure on a scale.
Heavy machinery operators, farmers, and builders can use 7 pounds per gallon for red diesel. A 50 gallon tank on an excavator holds about 350 pounds of fuel, just like the clear kind.
Remember that red diesel is not legal in a highway truck. Inspectors can check your tank, and fines can be steep.
Final Thoughts
Use 7 pounds per gallon for #2 diesel, red diesel, and most blends, and you will be close enough for almost every load plan. Add 9 pounds per gallon for DEF, check your axles on a certified scale, and you stay legal at the weigh station.
