Federal Truck Size and Weight Limits
This guide sets out the federal weight and size limits for commercial motor vehicles on the Interstate System and the regulation from which each limit is taken. The figures are those against which MaxLoader checks a load.
Source 23 CFR part 658 and 23 U.S.C. 127Figures verified against the published regulation on November 1, 2026
Scope
The federal weight limits apply to vehicles operating on the Interstate System. They are established by 23 U.S.C. 127 and set out by the Federal Highway Administration in 23 CFR 658.17. A State may not permit vehicles exceeding these limits to operate on the Interstate System, except as specifically provided by law.
On roads outside the Interstate System, weight limits are set by each State. They may be lower than the federal limits, particularly on local roads and posted bridges, and a State may authorize heavier vehicles by permit. A load plan that satisfies the federal limits is therefore lawful on the Interstate System; operation on any other road is subject to the limits of the State concerned.
Weight limits
A vehicle operating on the Interstate System must satisfy each of the following limits at the same time.
| Limit | Maximum | Regulation |
|---|---|---|
| Gross vehicle weight | 80,000 lb | 23 CFR 658.17(b) |
| Single axle | 20,000 lb | 23 CFR 658.17(c) |
| Tandem axle | 34,000 lb | 23 CFR 658.17(d) |
| Any group of two or more consecutive axles | As given by the bridge formula | 23 CFR 658.17(e) |
Gross vehicle weight is the total weight of the vehicle and its load, including the power unit, the trailer, fuel, the driver and the cargo. The axle limits apply separately to each axle and to each group of axles. Compliance therefore depends on the position of the cargo as well as on its total weight, and a vehicle may be within the gross weight limit while exceeding the limit on an individual axle or axle group.
Single axles and tandem axles
23 CFR 658.5 defines axles by the distance between their centers rather than by their construction. Single axle weight is the total weight transmitted to the road by all wheels whose centers may be included between two parallel transverse vertical planes 40 in apart. It is limited to 20,000 lb.
Tandem axle weight is the total weight transmitted to the road by two or more consecutive axles whose centers may be included between parallel vertical planes spaced more than 40 in and not more than 96 in apart. It is limited to 34,000 lb.
Axles spaced more than 96 in apart do not constitute a tandem axle. Each such axle is subject to the single axle limit, and the group is subject to the bridge formula.
Bridge formula
The bridge formula limits the weight on any group of two or more consecutive axles according to the number of axles in the group and the distance between its outer axles. Its purpose is to protect highway bridges, which are stressed less when a given weight is distributed over a greater length and a greater number of axles. The formula applies to every group of consecutive axles on the vehicle, not only to the vehicle as a whole.
By exception, two consecutive sets of tandem axles may carry 34,000 lb each, a total of 68,000 lb, provided that the distance between the first and last axles of the two sets is 36 ft or more. This exception permits a standard five-axle tractor-semitrailer to carry the full tandem axle limit on both its drive tandem and its trailer tandem.
The application of the formula is described in Federal Bridge Gross Weight Formula.
Vehicle dimensions
| Dimension | Federal limit | Regulation |
|---|---|---|
| Width | 102 in, or 2.6 m (102.36 in) | 23 CFR 658.15(a) |
| Length of a semitrailer | A State must permit at least 48 ft | 23 CFR 658.13 |
| Overall length of a tractor-semitrailer | No limit may be imposed by a State | 23 CFR 658.13 |
| Height | No federal limit | – |
The width limit applies on the National Network, and no State may impose a different width. The length provisions apply to tractor-semitrailer combinations only; the length of a straight truck is regulated by each State. Height is regulated by each State, commonly at between 13 ft 6 in and 14 ft.
Weight allowances
Federal law permits additional weight on the power unit in the following cases. Neither allowance increases any limit applicable to the trailer alone.
| Allowance | Maximum | Law |
|---|---|---|
| Idle reduction technology, such as an auxiliary power unit | 550 lb, or the certified weight of the unit if less | 23 U.S.C. 127(a)(12)(B) |
| Power unit fueled primarily by natural gas or powered primarily by battery-electric power | 2,000 lb, subject to a maximum gross vehicle weight of 82,000 lb | 23 U.S.C. 127(s) |
The idle reduction allowance requires written certification of the weight of the unit, and the operator must be able to demonstrate that the unit is fully functional. 23 CFR 658.17(n) continues to state the former figure of 400 lb; the statute has provided for 550 lb since 2012 and prevails.
Axle and tire ratings
Compliance with the federal limits does not permit an axle to carry more than its manufacturer's rating. 23 CFR 658.17(f) permits a State to limit a steering axle to the rating established by the manufacturer where that rating is lower than the federal limit. Under 49 CFR 393.75(g), no motor vehicle may be operated on tires carrying a weight greater than their rated load. On many tractors, the steering axle or tire rating, rather than the federal single axle limit, is the controlling limit at the front of the vehicle.
Exclusions
Federal Interstate System limits only. Weights above these figures are lawful on the Interstate in ways this tool does not model, among them: emergency vehicles (127(r)); heavy-duty tow and recovery vehicles taking a disabled vehicle to a repair facility (127(m)); longer combination vehicles a State allowed before June 1, 1991 (127(d)); weights a State authorized before July 1, 1956, or under a grandfathered formula, and has kept (23 CFR 658.17(i)); the route provisions of 23 U.S.C. 127 and 23 CFR 658.17 for particular Interstate routes, such as I-68 in Maryland and I-99 in Pennsylvania (658.17(j) and (m)); and permits. Off the Interstate System each State sets its own limits.
Permits for oversize and overweight vehicles are issued by the States for specified routes and periods. The Federal Government does not issue such permits.
Plan a load against these limits. See also Maximum Authorized Weights in the European Union.