What Is the Legal Length for a Semi Truck and Trailer?

Author: HALIM
Updated On:

Although people may not like driving near semi-trucks, they are an essential part of the US economy.

They are the reason you get meat for medium-rare steaks, your cereal for breakfast, and gas for your cooking station. There is no question that semi-trailers are grand and impressive in appearance.

You might, to some degree, know about trailer weight and height restrictions, but what about the legal length for a semi-truck and trailer?

Every state has laws regarding semi-truck length. It doesn’t matter if a truck is on a highway or small service road; it has to follow the length restrictions.

The reason behind such restrictions is to prevent overloading to avoid accidents and road damage. Let’s dive into more details and see how long a semi-trailer must be to stick with federal and state rules.

Semi Truck

Length of a Semi-Truck

Multiple factors play a role in determining the dimensions of a semi-truck. Federal laws have different implications, while state laws have something else to offer. Each truck might have a slight difference with all the factors in place.

On average, a semi-truck in the U.S.A is 72 ft long and 8.5 ft wide, and 13.5 ft tall. However, this size might go up to 60 ft or even less in some states. The maximum gross weight they can have is 80000 lb. 

While choosing a truck for transport or purchase, you must check the rules allowing the truck to enter the area. Choosing the wrong size might complicate things, as you’ll require a permit and other special arrangements.

When calculating the length of a truck, most people take measurements from the bumper to the back of the cab. American semi-trucks are 72 ft long if you measure it from the bumper to the trailer back. However, a semi-truck is only 10 ft long if measured from the bumper to the back of the cab.

With add-on boxes, a long hood, and sleepers, the cab length can have extra 2-6 ft, making the overall length around 12-16 ft. The average BBC (bumper-to-back cabin) length is 9-10 ft if such additions are not included.

Length of a Semi-Trailer

How long a semi-trailer is indicative of its capacity. The length of a semi-trailer is directly proportional to how much stuff it can accommodate without overloading.

Also, we can predict the maximum distance a semi-trailer can cover with its lengths. Most people often mix up the length with dimensions. This is somehow related but not necessarily the same thing. 

Now, the accurate method to measure how long your trailer is not exactly known to many people. All you need to do is to grab a measuring tape. Typically, it is measured from the front of the axle to the back side of the trailer. 

While we are on it, you need to keep a few things in mind while taking measurements. For starters, always take measurements from the outer wall. On average, this length is 27-31 ft.

Here is the thing, generally, there are no limits on how short 18-wheelers or big rigs can go, but there are limits on the maximum length. Tractor-trailer length varies in different models but ranges between 40-45 ft in most cases.

Another factor that impacts the length is the state and federal guidelines. CLICK HERE to learn about semi 18 wheeler rentals!

Lengths of Semi-Truck Based on Configurations

Gross weight is the main characteristic of classifying a heavy vehicle as a semi-truck. If the gross weight of a vehicle exceeds 10000 lb, we can call it a semi-truck.

This figure has been fixed by the Federal Motor Carrier Safety Administration(FMCSA). These limits vary from configuration to configuration of semi-trucks. Let us discuss dominant configurations that are common in America and their lengths. 

  • Combination Trucks

Combination trucks are the most common commercial trucks that exist in America. It is also referred to as an 18 wheeler in different areas.

The combination truck is formed by integrating a tractor with a semi-trailer. The tractor serves as the power unit, which determines the operation of the combination truck.

For instance, a tractor can be a sleeper cab, which is best suitable for long traveling. There is a small living area or sleeping berth in the tractor in case of a sleeper cab.

On the contrary, combination trucks with day cabs tractors are usually better for short-timed operations such as delivery or pick-ups. The lengths of combination semi trucks range between 43 and 53 ft. However, some states do approve up to 59 ft. 

  • Straight or Single-unit Trucks

In the case of straight or single-unit trucks, the distinguishing feature is that the power unit permanently mounts a single chassis. This configuration is most commonly used to deliver tons of parcels and supplies such as beverages, mixing concrete, and other construction works.

The chief purpose of straight or single-unit trucks is to move out heavy furniture when a family wants to shift houses.

Talking about the length, these trucks are somewhat shorter, with an average length of around 15-24 ft. Maximum length can go as long as 60 ft, and it depends on the State you reside in. Most states allow only up to 40-45 ft.  

  • Longer Combination Vehicles

Longer combination vehicles, or LCVs, are rare because these only operate in states where a gross weight of 80000 lb is permitted. LCVs are favorable because of their high productivity and lower costs.

Since they are bigger and spacious, more cargo can be loaded and transported, saving fuel costs and hiring drivers. Drawbacks include risks of accidents and lack of parking spaces. The maximum length of longer combination vehicles reaches up to 65 ft or even more. 

Semi Truck

How Important Are the Dimensions of a Semi-Trailer?

No doubt less attention goes to what dimensions a semi-trailer has; it is essential to consider them since they correlate to the weight they can carry. Their primary function, transporting cargo, is directly dependent on their dimensions.

For transportation purposes, note your semi-trailer length, width, and height. Step-deck semi-trailers that are 10ft. 6 inches high and about 8.5 ft wide can carry up to 48 and 65 tons.

Another example is the dry van semi-trailers, typically available for the transportation of house equipment and appliances since they are longer than other semi-trailers. 

Furthermore, the key thing to know when it comes to figuring out the length of a semi-trailer, as mentioned above, is that every state has particulars when deciding the semi-trailer length.

Not all states have the same length defined for a semi-trailer; rather, there are deviations. For instance, the U.S does not allow trailer lengths below 53 ft, especially on interstate and access roads.

In contrast, less than 53 ft semi-trailers can easily fuel transportation on roads not funded by the federal government.

For Alabama, the maximum trailer length is about 57 ft, whereas, in New York, it is 53 ft. In Virginia, the length is 48 ft; alternatively, it is 59 ft in Texas. 

So yes, state and federal laws are the governing bodies for the lengths of semi-trailers, and if they tell you about the defined regulations of various states, you will not face any legal issues. Hence, unquestionably, along with the width, the length of semi-trailers is very important.


1. What is the longest trailer length when it comes to tractor-trailers?

The average length of a tractor-trailer is usually between 40-5 ft. However, this depends on the state guidelines related to the trailer length dimensions and the trailer model.

2. How long is a flatbed semi-trailer?

A flatbed semi-trailer is one of the most common semi-trailer types. It is because of how budget-friendly they are. It typically comprises a 48-53 ft bed with an elevation of around 42-60 inches.

A good feature of flatbeds is that both dock dimensions and the trailer vary from type to type. Thus, you can adjust them accordingly, and that too with ease.

3. Does the length of a trailer have a relation with CDL?

In America, not many people are familiar with CDL law. CDL stands for a commercial driver’s license. The federal requirements of towing are not much restricted to the length of the trailer. They are more concerned with the weight of the trailer.

Most states will not bug you for a permit when you tow a 45 ft trailer without having a commercial driver’s license. However, you should expect trouble if you have an overloaded trailer or carry massive goods. It is generally a good choice to acquire CDL as soon as possible for your safety and to avoid future inconveniences. 

4. What is kingpin length?

Kingpin length is a common terminology in the measurement of trailers and semi-trucks. It is a standard measurement to check for road truck length restrictions.

It is a distance measure from the pivot of the fifth wheel connection to the center of the axle towards the rear side. Kingpin length determines the turning radius of the vehicle. The larger the kingpin length, the greater the turning radius, and vice versa. 


Moving heavy and larger loads is a headache experienced by many transporters. And therefore, the semi-trailers make it an easy task based on your current needs.

It’s better to acknowledge and go down the path of getting to know the different types for easy work. To make yourself on top of the transportation rules and regulations, it is commendable that you stay in touch or up to date with the specified dimensions of semi-trailers. 

This will help you understand which type of luggage you can transport to which place by which semi-trailer and also help your pace in work life more effectively. Not only does it provide that, but it is beneficial in helping you avoid unnecessary legal issues.

Many semi-trailer experts know of the cross-state border, types of semi-trailers, their specified dimensions, the expected affordable load of each semi-trailer, renting or purchasing a semi-trailer, and the laws.

It would be easier and more comfortable to go for an expert to help you navigate unless and until you become quite familiar with experience over the years.


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