80,000 lbs. After that, an oversize permit is required.
Gross weight or loaded weight is 80,000 lbs. Empty weight differs greatly depending on different tractor and trailer configurations but is around 36,000 lbs for a tractor and dry van trailer
The cargo, the trailer, and the weight of the vehicle.
Gross Vehicle Weight
For a standard five axel tractor trailer, the max is 80,000 lbs
Gross combination weight rating (GCWR) is the maximum weight limit determined by the vehicle manufacturer, including the weight of the vehicle, passengers, cargo, and towed trailer. Gross combination weight (GCW) is the actual measured weight of the vehicle, passengers, cargo, and trailer when fully loaded. The GCWR is a set limit, while the GCW can vary based on how the vehicle is loaded.
The length doesn't matter as much as the Gross Vehicle Weight Rating of the trailer and the Gross Combined Weight Rating of the combination of vehicle + trailer, as well as its use.
In most parts of the United States, a loaded tractor-trailer (also called a Class 8 commercial vehicle) can have a maximum loaded weight (Gross Vehicle Weight Rating, or GVWR) of 80,000 lbs, or 40 tons. Unloaded, depending on the type of tractor and trailer, the truck might weigh roughly between 25,000 and 40,000 lbs.
A typical tractor trailer unit, with a total of five axles, can typically carry between 23 and 25 tons legally, dependent on the tare weight of the tractor and trailer. The legal interstate gross weight rating for such a setup is 80,000 lbs.
The Gross Vehicle Weight (GVW) of a vehicle/trailer is the total weight of a fully loaded vehicle/trailer with maximum number of passengers allowed, maximum number of cargo allowed, full tank of gas, etc that the vehicle should weigh at maximum.
Gross Vehicle Weight is what a vehicle weighs at any given time. If you drove onto a scale you would see your present Gross Vehicle Weight. It can change depending on what you have in the vehicle (gas, passengers, cargo) and the tongue weight (the weight the tongue of a trailer places on your hitch) of any trailer you may be towing. Gross Vehicle Weight Rating is the maximum allowable total weight of a your vehicle when loaded - i.e including the weight of the vehicle itself plus fuel, passengers, cargo, and trailer tongue weight. It is considered unsafe to exceed your vehicles GVWR and may void your warranty. Curb Weight is what a vehicle weighs when empty.
If the Gross Combination Weight Rating (the combined Gross Vehicle Weight Rating of the truck and of the trailer) is in excess of 26,000 lbs., you can use it to test for a Class A CDL. However, you'll receive an "L" ("no air brakes") restriction, which will prohibit you from operating a CMV equipped with air brakes (such as a tractor-trailer).
Gross Vehicle Weight Rating, or GVWR is the rating given to a vehicle by the manufacturer. It can usually be found on the door pillar post (open the door and look for the sticker). Gross Combination Weight Rating is normally the weight assigned to a power unit (Truck Tractor) when speaking in terms of the weight of itself and the trailer. GCWR most generally would be 80,000 lbs., for a standard over the road truck configuration.