What is the axle limit for a truck?
In the United States, the most common axle limits place a cap of 20,000 pounds on a single axle and 34,000 pounds on a tandem axle, with an overall gross weight limit of 80,000 pounds on interstate highways. Exact figures can vary by state and by vehicle configuration, and heavier loads typically require permits.
How axle limits are determined
Truck weight limits are not a single fixed number. They depend on the number of axles, the distance between them, the road type, and the applicable regulatory framework. The per-axle caps (for example, single vs. tandem axles) set the baseline, while multi-axle loads are governed by formulas that account for axle spacing.
Key concepts you should know
The following outlines the core elements that shape axle limits in the United States, where rules are most widely cited.
In the United States, the baseline numbers you’ll encounter are:
- Single axle: up to 20,000 pounds (9,072 kg).
- Tandem axles (two axles in a line): up to 34,000 pounds (15,431 kg).
- Multi-axle groups: governed by the Federal Bridge Formula and axle spacing; there isn’t a single fixed number for all configurations.
Note: Some states set lower limits on non-interstate routes, and certain routes may require permits or special routing for heavier loads.
Permits, routing, and enforcement
Beyond the basic per-axle limits, many commercial operations rely on permits and route planning to move heavier loads legally. The system often involves calculating allowable weight for three or more axles based on spacing, and it can require specialized equipment or alternate routes.
To navigate these rules, operators should consider:
- Overweight permits: States issue temporary or trip-specific permits that authorize loads above standard limits on approved routes.
- Bridge and spacing considerations: The maximum weight for three or more axles depends on axle spacing and the number of axles, as determined by the Bridge Formula.
- Route class and road quality: Interstate highways typically enforce the 80,000-pound gross limit, while some state and local roads may have lower limits or require permits.
Always verify permit terms, route restrictions, and enforcement requirements before planning a heavy-haul trip.
International context
Axle and gross weight limits vary around the world. Many countries use a per-axle limit paired with a national gross weight cap, but the exact numbers, enforcement practices, and permit processes differ. If you’re operating internationally, consult local regulations and obtain any needed permits well in advance.
Summary
Axle weight limits are a function of jurisdiction, vehicle configuration, and road type. In the United States, the most common baseline is 20,000 pounds per single axle and 34,000 pounds per tandem axle, with an overall 80,000-pound gross weight limit on interstate highways. Multi-axle loads are regulated by the Federal Bridge Formula and may require permits and careful route planning. Always check state-specific rules and obtain the appropriate permits before transporting heavy loads, whether operating domestically or internationally.
