How long is a semi-truck allowed to be?

Federal law sets no overall length limit for a truck tractor pulling a semitrailer on the National Network. What it fixes is the trailer: no State may set a limit of less than 48 feet for the semitrailer in a tractor-semitrailer combination, or less than the longer length that State allowed on December 1, 1982, as listed in Appendix B of 23 CFR Part 658. States may not limit the distance between the axles of the tractor either.

How wide is a semi-truck allowed to be?

102 inches, or its approximate metric equivalent of 2.6 meters (102.36 inches), on the National Network; no State may set a width limit of more or less than that, except Hawaii, which keeps its 108-inch maximum. Mirrors, turn signal lamps, handholds and some other devices are excluded from the measurement, and States may grant special permits for wider vehicles.

How tall can a semi-truck be?

There is no federal height requirement for commercial motor vehicles, so each State sets its own. FHWA says most height limits range from 13 feet 6 inches (4.11 meters) to 14 feet (4.27 meters), with exceptions for lower clearance on particular roads.

Are 53-foot trailers legal?

The federal rule requires States to allow at least 48 feet, or the length they allowed on December 1, 1982. Appendix B of 23 CFR Part 658 lists those grandfathered lengths: 53 feet or more in 24 of the 52 listed jurisdictions (our count), up to 59 feet 6 inches in Louisiana and Oklahoma. California, Indiana and Wisconsin, listed at 48 feet or 48 feet 6 inches, also let semitrailers up to 53 feet run without a permit if they meet a kingpin-to-axle distance. Elsewhere the answer depends on the State's own law, which this page does not cover.

How long can double trailers be?

In a truck tractor-semitrailer-trailer combination, no State may set a length limit of less than 28 feet on either trailer, may not set an overall length limit on the combination, and may not prohibit such combinations on the National Network. Trailers of 28 feet 6 inches that were in lawful operation on December 1, 1982, must still be allowed if the combination is no longer than 65 feet overall.

Does the federal length rule apply to straight trucks?

No. FHWA says trucks that carry cargo on the same chassis as the power unit, commonly called straight trucks, are subject to Federal weight rules on the Interstate System and Federal width rules on the National Network but not to Federal length rules, which remain with the States. A straight truck towing a trailer is also subject to State length rules, except that its two cargo-carrying units may not exceed a federally set 65 feet.

Semi-truck dimensions: the federal length, width and height rules

Federal law does not set a maximum overall length for a semi-truck on the National Network. It works the other way round: no State may set a length limit of less than 48 feet on the semitrailer of a tractor-semitrailer, or less than 28 feet on each trailer of a twin combination, and no State may cap the overall length of either combination. Width is fixed at 102 inches (2.6 meters) on the National Network. There is no federal height limit at all; the States set their own, most of them between 13 feet 6 inches and 14 feet.

Status: 30 September 2026. This page follows 23 CFR Part 658 as published in the eCFR with the issue date of September 23, 2026 (sections 658.13 on length, 658.15 on width, 658.16 on exclusions, and Appendix B on grandfathered semitrailer lengths), and the Federal Highway Administration’s pamphlet Federal Size Regulations for Commercial Motor Vehicles, which paraphrases the regulations; in case of a dispute the regulations govern. The federal rules apply on the National Network and on reasonable access routes between it and terminals and facilities for food, fuel, repairs and rest. State rules on other roads are not covered.

Length

The federal length provisions apply only to two combinations, and only on the National Network or in transit between it and terminals or service locations (section 658.13(a)). FHWA describes them as “principally minimums that States must allow”.

Federal length rules, 23 CFR 658.13 (eCFR, as of September 23, 2026).
Vehicle	Federal rule
Truck tractor-semitrailer	No State length limit of less than 48 feet on the semitrailer, or less than the State’s grandfathered length in Appendix B; no overall length limit
Truck tractor-semitrailer-trailer (twin trailers)	No State length limit of less than 28 feet on either trailer; no overall length limit; the combination may not be prohibited
Twin trailers in use on December 1, 1982	Trailers of 28 feet 6 inches must be allowed if in actual and lawful operation on that date and the combination is no more than 65 feet overall
Bus	No State length limit of less than 45 feet on the National Network

FHWA adds that a State may not impose an overall length limit on a truck tractor pulling a single semitrailer, even if the trailer is longer than the federal minimum, nor a limit on the distance between the axles of the tractor. Where a State described its 1982 semitrailer limit as a distance from the kingpin to the rearmost axle or to the end of the semitrailer, any semitrailer meeting that description must be allowed (section 658.13(c)).

Specialized equipment. Section 658.13 sets its own figures for a few vehicle types, among them: at least 65 feet overall for traditional automobile and boat transporters and 75 feet for stinger-steered ones; exactly 97 feet for drive-away saddlemount combinations; for maxi-cube vehicles at least 34 feet for either cargo box, 60 feet from the front of the first to the rear of the second box and 65 feet overall; and at least 75 feet for munitions carriers using dromedary equipment.

The 53-foot trailer and the grandfathered lengths

Appendix B to Part 658 lists the semitrailer lengths each State must continue to allow because they were in actual and lawful use there on December 1, 1982. They are lengths a State may not prohibit, not maximums, and FHWA says the federal length limits are principally minimums.

Grandfathered semitrailer lengths, Appendix B to 23 CFR Part 658 (feet-inches), grouped by length.
Length	States and jurisdictions
48-0	Alaska, California, Connecticut, District of Columbia, Florida, Georgia, Hawaii, Idaho, Maine, Maryland, Massachusetts, Michigan, Minnesota, New Hampshire, New Jersey, New York, North Carolina, Puerto Rico, South Carolina, Utah, Vermont, Virginia, Washington, West Virginia, Wisconsin
48-6	Indiana, Rhode Island
50-0	Tennessee
53-0	Delaware, Illinois, Iowa, Kentucky, Mississippi, Missouri, Montana, Nebraska, Nevada, North Dakota, Ohio, Oregon, Pennsylvania, South Dakota
53-6	Alabama, Arkansas
57-4	Colorado, Wyoming
57-6	Arizona, Kansas, New Mexico
59-0	Texas
59-6	Louisiana, Oklahoma

Three footnotes in the appendix deal with the 53-foot semitrailer where the listed length is shorter: in California, semitrailers up to 53 feet may operate without a permit with a kingpin-to-rearmost-axle distance of 38 feet; in Indiana, with a kingpin-to-rearmost-axle distance of 40 feet 6 inches; in Wisconsin, with a kingpin-to-rear-axle distance of 41 feet measured to the center of the rear tandem assembly. In all three, a semitrailer used for motorsports vehicles under section 658.13(g) may run without a permit if the kingpin is no more than 46 feet from the center of the rear axle. Outside Appendix B, whether a 53-foot semitrailer may run on a given road depends on the State’s own law, which this page does not cover. How European semitrailers are sized is explained in semi-trailer dimensions.

Width

No State may impose a width limit of more or less than 102 inches, or its approximate metric equivalent of 2.6 meters (102.36 inches), on a vehicle operating on the National Network; Hawaii keeps its 108-inch maximum (section 658.15). The rule does not apply to special mobile equipment, and a State may grant special use permits to vehicles, including manufactured housing, that are wider than 102 inches. FHWA’s pamphlet traces the figure back: the Federal-Aid Highway Act of 1956 set 96 inches on the Interstate System, the 1976 Act allowed 102 inches for buses, and the Surface Transportation Assistance Act of 1982 extended 102 inches to trucks.

Height

“There is no Federal vehicle height requirement for CMVs”, FHWA’s pamphlet says, so States set their own height restrictions. Most height limits range from 13 feet 6 inches (4.11 meters) to 14 feet (4.27 meters), with exceptions for lower clearance on particular roads. The pamphlet gives no State-by-State list, and none is given here.

What is left out of the measurement

Section 658.16 says every component is measured unless law or regulation excludes it, and lists the exclusions:

rear view mirrors, turn signal lamps, handholds for getting into and out of the cab, splash and spray suppressant devices and load-induced tire bulge;
non-property-carrying devices at the front of a semitrailer or trailer, devices that extend no more than 3 inches beyond each side or the rear, devices needed for loading or unloading that extend no more than 24 inches beyond the rear, and the devices listed in Appendix D;
resilient bumpers extending no more than 6 inches beyond the front or rear;
aerodynamic devices extending up to 5 feet beyond the rear, if they cannot damage a vehicle or injure its passengers in a rear impact and do not obscure lamps, placards or conspicuity markings.

Each exclusion is specific and may not be combined with another, and measurements are made from a point on one side or end of the vehicle to the same point on the opposite side or end. How Europe treats aerodynamic devices and cab length is covered in aerodynamic cabs and length rules.

Straight trucks

FHWA’s pamphlet says trucks that carry cargo on the same chassis as the power unit and cab, commonly known as straight trucks, are subject to federal weight requirements on the Interstate System and federal width requirements on the National Network but not to federal length requirements; their length is regulated by the States. A straight truck towing a trailer or semitrailer is likewise subject to State length rules, except that the total length of its two cargo-carrying units may not exceed a federally established limit of 65 feet. The federal weight limits are described in how much a semi-truck weighs.

What this page does not cover

State length, width and height rules beyond Appendix B, including the roads outside the National Network.
Oversize permits in detail.
The length and weight freeze on longer combination vehicles under the Intermodal Surface Transportation Efficiency Act of 1991.
Weights, covered on a separate page.