Ever wondered how many gallons a semi-truck holds? Pro tip: Filling your tank to 100% may not be the best for your truck.

Semi-truck drivers, operators, and fleet managers: if you’re wondering how many gallons a semi truck holds — as well as how to maximize fuel economy — you’ve come to the right place.

We’re Certified Fleet Services, Florida’s go-to diesel truck repair provider for fleets large and small. If you’ve asked yourself, “How many gallons does a semi-truck hold?” and received conflicting responses, we understand.

Rest assured, we’ll give you the quick answer: 120-150 gallons. But, there’s so much more to the question than that.

We’re here to give you the straight facts and Certified answers to all your fuel economy-related questions. Join us for this quick round-up article all about gasoline in semi-trucks. Let’s help you create a smoother, more efficient truck operation.

The 95% and 25% rules, and the gas a semi-truck can hold

When it comes to semi-truck fuel, filling up a semi-truck’s tank to 100% isn’t advisable. Whether your truck has two 120 or two 150-gallon tanks under the cab, you’ll want to fill your tank to 95% capacity.

We call this the 95% rule. The reason why we recommend filling a tank to 95% of its capacity is to help with the following:

• Avoid the risk of spills: leave a little bit of room for air inside a tank. Otherwise, the overfilled tank could spill out diesel fuel via overflow valves. What’s more, spilled fuel can be harmful to the environment and can pose a health and safety risk for nearby drivers.
• Diesel expansion: Since diesel fuel expands and contracts based on the temperature outside, filling a tank could have devastating consequences. Since suction components aren’t built to process tons of fuel from the bottom of a gas tank, drivers could be losing out on fuel efficiency if they drive on more than 95% of their fuel capacity. For example, imagine driving in the dead of winter on excess fuel only to find that the water in the fuel lines prevents gasoline from reaching the engine.

Driving on a tank that’s near empty also poses problems. At Certified Fleet Services, our drivers and ASE-certified technicians don’t allow their fuel tanks to go below empty — and most truck drivers won’t let their tanks to fall below 25% of total fuel capacity.

The reason? Contaminants like dirt and bacteria can build up at the bottom of a fuel tank. If you drive your truck on the empty fuel sign often, you could hurt internal components like the engine, fuel pump, catalytic converter.

To keep your fleet healthy and strong, make sure to adhere to the 95% and 25% rules — that is, filling your tank up to 95% capacity and not allowing it to fall below 25% capacity.

Other reasons for the 95% rule with gas in a semi-truck

The major reason for keeping the gasoline and diesel in a semi-truck, tanker, trailer, and vehicle at 95 percent of its capacity is to decrease spills and potential leaks. Since crude oil (and liquids) tends to expand in hot temperatures, leaving five percent of each of the two fuel tanks empty will give you a fighting chance at saving more and wasting less fuel.

By not filling a tank to 100% capacity, you’ll likely get the same miles per gallon (MPG) on a 95% filled tank as you would with a 100% filled tank. And better fuel consumption is always a win.

Just the facts (with trucks and trailers…)

Truck Fact #17: Did you know that a semi-truck’s engine can go for 1,000,000 miles before you even need to think about replacing it?

Best practices like not allowing fuel to exceed 95% of its capacity nor allowing fuel to drop to under 25% of its capacity will ensure your truck continues to haul loads on the road for miles and miles to come.

Understanding the weight of fuel per gallon in a semi-truck

You might be wondering, “Why is the weight of fuel per gallon important, especially if we’re talking about how many gallons of fuel semi-trucks hold?”

The reason fuel weight is important is because the knowledge of how much fuel weighs can give us insights into how to better manage our fleet.

Since the Federal Motor Carrier Safety Administration (FMCSA) created rules about weight restrictions for semi-trucks, being mindful of your truck’s overall weight will help you avoid fines and tickets with the Department of Transportation (DOT).

For example, factoring in the weight and size of the tank can help you better avoid tickets and run-ins with DOT inspections — and even help you with passing your next annual DOT inspection.

Truckers: let us explain. Let’s take a look at the weight of fuel.

Since a gallon of diesel fuel weighs about seven pounds, most diesel fuel tanks weigh anywhere from 840-1,065 pounds. Since the gross vehicle weight and cargo limit for semi-trucks is 80,000 pounds according to U.S. federal law, you’ll want to keep in mind how the amount of fuel affects your standing with the DOT during DOT inspections.

To reduce the total weight of your load, you may want to reconsider using one or two fuel tanks — or a more fuel-efficient truck altogether. By being mindful of weight, you’ll more likely be within the DOT’s acceptable limits for weight, and reduce any liability associated with not complying with federal DOT laws.

Less liability equals better fleet management.

Table: Main factors affecting how many gallons a semi truck can hold

Certified answers for all your semi-truck fuel needs

Most semi-trucks hold on average 120-150 gallons per tank. Depending on the size, make, model, and year of the truck, it will come with one or two fuel tanks.

We subscribe to the 95% and 25% rules:

• We fill our tanks to 95% of its capacity, and
• We don’t allow our tanks to drop below 25% of its capacity

Following these guidelines has helped us to reduce spills and prepare ourselves for the naturally occurring fuel expansion that results from temperature changes in the environment.

And we’re confident these guidelines can help you as well.

But, if you find that your truck is leaking oil, give us a call. Our ASE-certified master technicians would be happy to troubleshoot the issue with you and get you back on the road faster.

Until then, be well! We’re here for you for all your diesel truck repair-related needs.

Frequently asked questions about gasoline and semi-truck

How much gasoline do semi-truck gallons hold?

In general, newer semi-trucks have two fuel tanks. Each fuel tank carries about 120-150 gallons — or 450-560 liters — of fuel. 150 gallons is almost 1,065 pounds. That’s pretty heavy!

This weight adds up, especially when driving longer distances with heavy cargo.

How many miles can a semi-truck go on a gallon of gas?

The average motor vehicle today gets about 25.7 MPG. In contrast, recent data from Statista.com suggests that between 2016 to 2021, the average light-duty pickup truck clocked 18.9 to 19.4 combined city/highway MPG.

In general, the larger the vehicle, the fewer the MPG. As it stands, most semi-trucks clock in a paltry 7-8 MPG. All the more reason to make sure your truck is in peak condition. You can maximize the strength and quality of your vehicle by bringing your truck into your preferred diesel repair shop for corrective and preventive maintenance.

Doing so will ensure your semi-truck continues to operate at peak fuel efficiency.

What is the 95% rule for semi-truck fuel?

The 95% rule suggests that you shouldn’t fill up your fuel tanks more than 95% of their total fuel capacity.

Adhering to the 95% rule can help you avoid problems with fuel expansion and roadside oil spills.

How heavy is a full tank of gas in a semi-truck?

A tank that’s filled to 100% capacity can weigh anywhere between 850 to 1,065 pounds. Temperatures inside and outside of the truck can affect this number.

But, outdoor temperatures tend to affect the weight only by about half a pound (or less).