How many gallons does a tanker truck hold? Shell vs legal load

Tanker truck capacity: two numbers, not one

Every tanker has two capacities. The shell capacity is how much liquid the tank physically holds, stamped on its data plate. The legal capacity is how much you can carry before the truck goes over its weight limit. For anything heavier than about 5 lb a gallon, the legal number is the smaller one, and it is the one that matters on the road.

That is why the honest answer to "how much does a tanker truck hold" is a range and a formula. Dealer listings for aluminum DOT 406 petroleum trailers from LBT, Polar and Heil show shells of about 9,200 to 9,500 gallons in four or five compartments. Source The makers don't publish gallon figures on their own sites, so check the data plate on the tank you're pulling. DOT 406 is the low-pressure spec built for products like gasoline and diesel. Source

How many gallons of fuel does a tanker truck hold?

Fuel weight decides it. Gasoline has a specific gravity of 0.72 to 0.76, about 6.0 to 6.3 lb a gallon. Source Diesel runs about 0.841, roughly 7.0 lb a gallon. Source Divide your legal payload by the weight per gallon and you have your gallons.

The federal limit on the Interstate is 80,000 lb gross unless the bridge formula sets a lower number. Source Some states allow more on their own roads or with permits, and a lighter tractor and trailer add payload. Every 1,000 lb shaved off the empty rig is about 160 more gallons of gasoline. That is why fuel haulers pay for aluminum trailers and light tractors.

The math, step by step

1. Gross limit 80,000 lb minus the empty rig 32,000 lb = 48,000 lb of legal payload.
2. Gasoline at 6.2 lb a gallon: 48,000 ÷ 6.2 = 7,741 gallons.
3. Fill the whole shell at 99% instead (9,207 gal × 6.2 = 57,083 lb) and the truck grosses 89,083 lb: overweight by 9,083 lb.
4. Check axle groups too: a legal gross with too much in the front compartment can still put the drive axles over.

Run your own load through the tanker weight calculator, and check axles with the truck weight limit checker.

Outage: why the top of the tank stays empty

Liquids grow as they warm. A load poured cold at the rack will expand on a hot afternoon, so federal rules require at least 1% outage, empty space, in each tank or compartment at the reference temperature: 115 F for an uninsulated tank, 105 F for an insulated one. Materials poisonous by inhalation need 5%. Source On a 9,300 gallon shell, 1% is 93 gallons. In practice weight limits leave far more room than that on gasoline and diesel.

Partly full compartments bring their own risk: surge, the wave of liquid that pushes the truck when it brakes or turns. Baffled and compartmented tanks break the wave up; smooth-bore food-grade tanks don't. More in our tanker truck guide.

Capacity by tanker type

Straight tank trucks, the bobtails that deliver heating oil and propane to homes, carry far less than a semi tanker because a single truck's gross weight rating is much lower. Their capacity is set by the truck's GVWR and the axles under the tank, so read the plate on both.

How many gallons of gas in a tanker truck at the station?

A delivery to a gas station usually splits several grades across the compartments, regular, mid-grade, premium and diesel, sized to what each underground tank can take. The driver gauges the station's tanks before unloading so nothing overflows. A full trailer often supplies more than one station on the same trip, which is why compartment sizes matter as much as the total.

Splitting a load across compartments

Say a station orders 4,000 gallons of regular, 1,500 of premium and 2,000 of diesel on the five-compartment trailer from our example. The gasoline totals 5,500 gallons at 6.2 lb, about 34,100 lb; the diesel adds about 14,020 lb. That is 48,120 lb of product, 120 lb over the example payload, so the dispatcher trims the diesel by about 20 gallons or the carrier runs a lighter tractor. The order also has to fit the compartments: 2,000 gallons of diesel won't go in a 1,000 gallon pot, and products can't share one.

Reading a tanker's data plate

Every spec cargo tank carries a metal plate, usually on the front head or the frame near it. It lists the maker, the spec (DOT 406, 407, 412 or MC 331), the date built, the maximum allowable working pressure, the materials, and the capacity of each compartment in gallons. Test dates are stenciled nearby. Before you take a load in a tank you haven't pulled before, read the plate: the compartment sizes tell you what orders fit, and the spec tells you what products the tank may carry.

Common tanker capacity mistakes

• Loading to the shell, not the scale. A full shell of diesel on a standard rig is thousands of pounds over the gross limit.
• Using a generic weight per gallon. Products vary by blend and temperature; use the figure on the shipper's paperwork or safety data sheet.
• Forgetting the tractor's fuel. Full saddle tanks weigh close to a thousand pounds more than near-empty ones.
• Watching gross but not axles. Heavy product in the front compartment can overload the drives while the gross looks fine.
• Filling cold product to the top. It expands in the sun; outage exists for that reason.

License and rules that come with the gallons

A truck with tanks over 119 gallons each and 1,000 gallons or more in total is a tank vehicle, which needs the N endorsement on a CDL. Source Gasoline and diesel loads in those quantities are hazardous materials, so the driver needs X (tank plus hazmat) and the carrier needs the matching insurance and registration. We don't book placarded hazmat; on our desk, tanker work means water, food-grade, liquid and dry bulk loads that aren't placarded. Compare tanker types in types of tanker trucks.

Methodology

Shell capacities come from dated dealer listings that state the maker's model capacity, because the makers don't publish gallons on their own pages. Weights per gallon use NIOSH's specific gravity for gasoline (midpoint 0.744, 6.2 lb) and NOAA's for diesel (0.841, 7.01 lb), times 8.34 lb for a gallon of water. The 32,000 lb empty weight is an EXAMPLE, not a standard; weigh your own rig on a certified scale. We review this page every year.