Federal Truck Size and Weight Limits
On the Interstate, a truck may weigh up to 80,000 pounds, with 20,000 on one axle and 34,000 on a tandem (23 CFR 658.17). It must also pass the Federal Bridge Formula, which limits weight by axle spacing. The federal width limit is 102 inches on the National Network. There is no federal height limit. States set height and their own limits on other roads.
Facts checked October 16, 2026
Key Points
- On the Interstate, the gross weight limit is 80,000 pounds. The limit is 20,000 pounds on any one axle and 34,000 pounds on a tandem axle group (23 CFR 658.17(b), (c) and (d))
- A truck must also meet the Bridge Gross Weight Formula for two or more consecutive axles. Two sets of tandem axles may carry 34,000 pounds each if the first and last axle are 36 feet apart or more (23 CFR 658.17(e))
- States may not enforce lower Interstate weight limits than the federal ones, and the limits include all tolerances (23 CFR 658.17(f) and (g))
- States may not limit tire load to less than 500 pounds per inch of tire width, except on the steering axle. They may not limit the steering axle to less than 20,000 pounds or the maker's rating, whichever is lower (23 CFR 658.17(f))
- No state may set a width limit other than 102 inches on the National Network. Hawaii keeps 108 inches (23 CFR 658.15)
- No state may set a semitrailer limit below 48 feet, or a limit below 28 feet for each unit of a twin trailer combination. A state may not set an overall length limit on these combinations on the National Network (23 CFR 658.13)
- There is no federal height limit. Each state sets its own, and FHWA says most are between 13 feet 6 inches and 14 feet
Examples of the Federal Bridge Formula (23 U.S.C. 127)
| Maximum weight on the group | |
|---|---|
| 2 axles, 4 feet apart (a tandem) | 34,000 pounds |
| 5 axles, 36 feet apart end to end | 70,500 pounds |
| 5 axles, 40 feet apart end to end | 73,000 pounds |
| 5 axles, 51 feet apart end to end | 80,000 pounds (the gross limit) |
What are the federal weight limits for trucks?
The federal weight rules apply to the Interstate System and reasonable access to it (23 CFR 658.17(a)). The gross vehicle weight may not exceed 80,000 pounds, unless the bridge formula allows less. No single axle may carry more than 20,000 pounds. A tandem axle group may carry 34,000 pounds. These limits include all tolerances. The only allowance is for portable scales, which are generally accurate within 2 or 3 percent, and never more than 5 percent. A fine schedule that charges nothing up to a set weight, such as 1,000 pounds, is treated as a tolerance and is not allowed (23 CFR 658.17(g)). A truck with an auxiliary power unit or idle reduction unit may carry up to 400 more pounds, or the certified weight of the unit if less. The operator must prove the weight of the unit and that it works at all times (23 CFR 658.17(n)).
How does the bridge formula work?
The Federal Bridge Formula protects bridges by limiting the weight on any group of two or more axles. The limit is W = 500 x ((L x N / (N - 1)) + 12N + 36). W is the weight in pounds, rounded to the nearest 500. L is the distance in feet between the first and last axle of the group. N is the number of axles in the group (23 U.S.C. 127). More axles and more distance between them allow more weight. A tandem 4 feet apart gets 34,000 pounds. Five axles that span 40 feet get 73,000 pounds, which is 7,000 below the 80,000 pound cap. A five-axle truck needs about 51 feet between its first and last axle to carry the full 80,000 pounds. Two sets of tandem axles may carry 34,000 pounds each if the first and last axle are 36 feet apart or more. Total weight can never exceed 80,000 pounds.
How wide can a truck be?
No state may set a width limit of more or less than 102 inches on the National Network (23 CFR 658.15). Hawaii keeps its 108 inch limit. Some parts of the truck do not count toward width or length. They include mirrors, turn signal lamps, handholds, splash and spray devices and load-induced tire bulge. Small non-cargo devices that stick out no more than 3 inches on each side are also left out (23 CFR 658.16). A state may issue special use permits for wider vehicles. Each exclusion stands alone. You cannot add them together.
How long can a truck and trailer be?
The federal length rules cover tractor-semitrailer and tractor-semitrailer-trailer (twin trailer) combinations on the National Network. No state may set a semitrailer limit under 48 feet, or a limit under 28 feet for each trailer in a twin combination. No state may set an overall length limit on these combinations. No state may ban twin trailer combinations (23 CFR 658.13). A state may not prohibit trailers that were lawful in that state on December 1, 1982, and states with older kingpin-to-rear-axle limits must allow trailers that meet them. A state may not set a limit under 45 feet on a bus. Many states allow longer trailers than the federal minimum. Check each state you run in.
How tall can a truck be?
There is no federal height limit. Each state sets its own, and FHWA says most states set it between 13 feet 6 inches and 14 feet. Some states allow more on certain roads. Check the limit for every state on your route before you load tall freight. Our low bridge lookup shows known low bridges near a route, but a bridge not on the list is not proof that a road is clear.
Where do the federal limits apply, and what is reasonable access?
The weight rules apply to the Interstate System. The length and width rules apply to the National Network. The Network is made up of the Interstate and other highways that FHWA lists for large trucks (23 CFR 658.9). Off the Network, states set their own limits. Even so, no state may deny large trucks reasonable access between the Network and terminals and facilities for food, fuel, repairs and rest (23 CFR 658.19(a)). No state may deny access within 1 road mile of the Network on the most reasonable route, except for specific safety reasons on a route. States may not apply blanket bans on 102 inch wide vehicles (23 CFR 658.19(d) and (f)).
When can you go over the limits?
States may issue special permits without regard to the axle, gross or bridge formula limits for loads that cannot be divided (23 CFR 658.17(h)). A few states and roads have grandfather rights for weights that were lawful under older state law (23 CFR 658.17(i)). Permit rules differ by state. They cover loads that are over width, length, height or weight. Our oversize permit estimator and scale guide can help you plan. Check each state's permit rules before you move the load.
Related Free Tools
Low Bridge Lookup
See known low bridges and overhead clearances near a place or in a state, checked against your truck's height. From the federal National Bridge Inventory.
Weight & Axle Load Calculator
Check federal axle weight limits and bridge formula compliance before you scale.
Scale / Weigh Station Guide
PrePass eligibility, what to do at a scale, violations, and a state-by-state guide.
Oversize / Overweight Permit Estimator
Check whether your load goes past the usual legal height, width, trailer length and weight, and when escorts often start.
Frequently Asked Questions
What is the legal weight limit for a semi truck?+
On the Interstate, 80,000 pounds gross, 20,000 pounds on a single axle and 34,000 pounds on a tandem axle group, and the weight must also pass the Federal Bridge Formula (23 CFR 658.17). States set their own limits on other roads.
What is the bridge formula?+
It limits the weight on any group of two or more axles by the number of axles and the distance between the first and last. The formula is 500 x ((L x N / (N - 1)) + 12N + 36), rounded to the nearest 500 pounds (23 U.S.C. 127).
How wide can a truck be?+
102 inches on the National Network. Mirrors, turn signal lamps and a few other devices are left out of the measurement (23 CFR 658.15 and 658.16). A state can issue special permits for wider loads.
Is there a federal height limit for trucks?+
No. Each state sets its own, and FHWA says most states set it between 13 feet 6 inches and 14 feet. Check the limit for each state on your route.
Does sliding my tandems change my weight limit?+
Sliding the tandems changes the weight on each axle and the spacing. The tandem limit stays 34,000 pounds, but the bridge formula can limit the total weight when the axles are close together. Spreading the axles farther apart allows more total weight. A five-axle truck needs about 51 feet between its first and last axle for the full 80,000 pounds.
Does an APU add to my weight limit?+
Yes, up to 400 pounds, or the certified weight of the unit if that is less. You must be able to prove the weight of the unit and that the idle reduction system works at all times (23 CFR 658.17(n)).
More federal trucking rules
- Hours of Service Rules for Truck Drivers
- ELD Mandate: Who Needs an ELD
- DOT Roadside Inspection Levels Explained
- DOT Drug and Alcohol Testing Rules
- Driver Qualification File Requirements
- DVIR and Vehicle Maintenance Rules
- New Entrant Safety Audit Requirements
- Hours of Service Exceptions and Exemptions
- Motor Carrier Insurance Requirements
- CDL Classes, Endorsements and ELDT Training
- DOT Physical and Medical Card Requirements
- Drug and Alcohol Clearinghouse Requirements
- Cargo Securement Rules for Trucks
- Hazmat Basics for Truck Drivers and Carriers
- USDOT Number and Biennial Update Requirements
- Safety Ratings, Compliance Reviews and DataQs
- California Clean Truck Check (HD I/M)
- Truth-in-Leasing Rules for Owner-Operators
- Form 2290 Heavy Highway Vehicle Use Tax
- Truck Driver Phone, Texting and Seat Belt Rules
- Railroad Crossing Rules for Truck Drivers
- Truck Emergency Equipment and Warning Triangle Rules
- Truck Windshield, Dash Cam and Mirror Rules
- CDL Disqualification: Major and Serious Offenses
- Truck Tire Rules: Tread Depth, Retreads and Pressure
- Trailer Reflective Tape (Conspicuity) Rules
- Truck Brake Rules: Pushrod Stroke, Lining Thickness and ABS
- Driver Conduct Rules: Alcohol, Drugs, Fatigue, Passengers and Pre-Trip Checks
- English Language Proficiency for Truck Drivers: The 391.11(b)(2) Rule
- Weigh Station Rules: Who Must Stop and What Happens If You Skip
- Truck Lighting Rules: Required Lamps and Reflectors (49 CFR 393)
- Driver Road Test Rules: The Company Road Test and Certificate (49 CFR 391.31)
Related terms and pages
Sources
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This is a plain-language summary for reference, not legal advice. Check the official rule text before you rely on any detail. Ask a compliance professional about your own operation.