A semi-truck is big, right? But how big? We may see these monsters on the highway but let’s look further at the dimensions of a semi-truck.

Semi-truck dimensions: All semi-trucks have similar dimensions as they need to adhere to transportation standards. The maximum width is 8.5 feet, the maximum height is 13.5 feet, and the maximum length is 53 feet. Without a trailer, however, the cab of a semi-truck is about 20 feet long. Semi-trucks have fuel tanks that hold up to 300 gallons of diesel. They only get about 5 miles per gallon, so the extra fuel is extremely important, especially if drivers are in rural areas.

Average semi-truck mpg

A semi-truck has a diesel engine with is more powerful than a gas engine. With a diesel engine, semi-trucks can pull their trailers which are loaded down with cargo.

Unfortunately, no matter how powerful the engine is, a semi-truck has a very limited mpg. In fact, the average semi-truck can only get 5 mpg. This is in contrast to a regular car which can get about 24 mpg.

The terrain of a road will greatly impact the average miles per gallon a semi-truck can get. Going uphill takes considerable effort, so a semi-truck drops down to about 3 mpg.

Downhill is easier and a semi-truck can get up to 20 mpg. However, going downhill means a loss of control so semi-trucks will be wise not to go too fast.

There are newer semi-trucks being built with more efficient engines. Some of the latest models offer between 8 and 10 mpg, which can result in considerable fuel savings.

Semi-truck height, width, length

The dimensions of semi-trucks have some figures that are very strict and others that have more room for negotiation.

The maximum width of a semi-truck is 8.5 feet and this is a pretty standard measurement. If a semi-truck is built wider than this, it can cause devastation as the truck needs to maneuver around other cars on the road.

For height, the maximum is 13.5 feet. Again, this is a very strict measurement.

Bridges, tunnels, and overpasses are all constructed to allow clearance for semi-trucks. If trucks were suddenly built taller, they would not fit under modern infrastructure and multiple crashes can happen.

Because this is the standard height, if there are any underpasses that are lower, they will be clearly marked and alternate routes posted.

Still, there are regular new reports of semi-trucks that are over their height limit crashing into low overpasses. This causes traffic snarls and extra repair jobs.

Finally, the length of a semi-truck is typically 20 feet, and if you are counting the trailer as well, typically an additional 48 or 53 feet. This is the one measurement that varies more and depends on the truck’s manufacturer and the purpose of needing the semi-truck.

There are plenty of trailers that are shorter than 48 feet as well, when you get into things like trailers for roll off bins, or rock and gravel haulers, grain haulers, etc.

Semi-truck weight

Completely empty, a semi-truck will weigh about 35,000 pounds. Each truck is different and this weight will fluctuate in accordance with the type of model it is.

For example, a refrigerated trailer will have more weight because of the apparatus needed to keep the contents cool.

There are federal laws that dictate how much a semi-truck can weigh. In America, this is a total of 80,000 pounds.

The total weight has to take into consideration the entire truck, including the fuel tanks. These standards are regularly checked and fines are issued if truck drivers are not in compliance.

The maximum weight of a semi-truck is incredibly important. If there is too much weight, it can cause severe issues on roadways.

Already you may notice slight dips in asphalt on roads that regularly see truck usage. If these grooves become too deep, the road needs to be repaved which costs taxpayers a lot of money.

Semi-truck horsepower

Semi-truck horsepower

A semi-truck has an engine with a horsepower of between 400 and 600. As for torque, it measures between 1,000 to 2,000 lb-ft.

In comparison, the average car has a horsepower of around 120, and larger trucks and SUVS will be closer to 200 hp.

The larger horsepower is obviously necessary as a semi-truck weighs so much more than the average car.

How many gears does a semi-truck have?

A semi-truck has 10 gears but some models have as many as 15 or 18 gears. Of these, two of them will be for reversing.

The bandwidth of a semi-truck’s gear is much smaller than with a car, which is why so many gears are needed. Truck drivers need to continually shift up and down as they change speed.

There are more trucks, however, that have an automatic transmission. This means drivers don’t need to change the gears manually.

How long is a semi-truck without a trailer?

There are two parts to a semi-truck: the cab which includes the engine and the driving area, and the trailer, which is where goods are stored.

Without the trailer, a semi-truck is about 20 feet long. This measurement starts at the very back, near where the trailer sits, and all the way to the front where the engine sticks out.

Trailer cabs will vary in size according to how much space is needed for rest. Some cabs have quite the outfit with a bed, TV, and storage area.

Some even have a custom sleeper cab that more resembles a camper than what you’d think would be part of a trailer cab. These semis are MUCH more expensive than the others.

Other trucks, which are built for shorter journeys, will only have a small bench behind the driving area. These cabs will be much shorter.

How many gallons are in a semi-truck tank?

The tank on a semi-truck will hold between 125 and 300 gallons of fuel. Many semi-trucks will have two fuel tanks, doubling this size up to 600 gallons.

A second fuel tank is important for many reasons. First, it means less stopping, which results in more money made for a truck driver.

Having extra fuel on board is especially important if a truck driver is driving through a rural area. As semi-trucks use a lot of fuel, they could potentially run out if there are issues on the road or a fuel stop no longer exists.


Semi-trailers are very large and measure up to 53 feet long and 13.5 feet high. They can weigh up to 80,000 pounds.