Truck weight limits: gross, axle and bridge formula rules

Weight limits decide how much freight a truck can carry and where it can go. They protect roads and bridges, and they affect safety, because an overloaded truck takes longer to stop and wears its brakes and tires faster. For owners, they also decide revenue: every pound of truck is a pound of freight you cannot haul.

The federal limits

Under 23 CFR 658.17, these limits apply on the Interstate System:

• Gross vehicle weight: 80,000 pounds
• Single axle: 20,000 pounds
• Tandem axle: 34,000 pounds
• Axle groups: limited by the federal bridge formula

Source: 23 CFR 658.17, checked October 2026

The rule also includes exceptions, such as grandfathered state limits and allowances for certain equipment. On roads off the Interstate System, states set their own limits, which can be higher or lower.

How weight is shared on a five-axle truck

The steer axle figure is a typical working value; your steer axle's actual limit is the lower of its rating, its tires' ratings and the legal limit. Add the three groups and a five-axle truck can reach 80,000 pounds only with the weight spread evenly.

The bridge formula

The federal bridge formula sets the maximum weight on any group of two or more consecutive axles:

W = 500 x [(L x N) / (N - 1) + 12N + 36]

where W is the maximum weight in pounds, L is the distance in feet between the outer axles of the group, and N is the number of axles in the group. The formula allows more weight when axles are spread farther apart. Short wheelbase trucks and closely spaced axle groups may be limited below the single and tandem figures.

For most standard five-axle tractor-trailers with normal axle spacing, the formula allows the full 80,000 pounds. It matters most for dump trucks, short trucks with several axles, and specialized equipment.

Checklist: staying legal on weight

Box trucks and straight trucks

For box trucks and straight trucks, the gross vehicle weight rating on the door label is the first limit: truck plus cargo must not exceed it. Axle ratings and legal axle limits also apply. A 26 ft box truck rated at 26,000 pounds may carry far less cargo than its box can hold, once the truck's own weight is subtracted. Our guide to the heavy duty truck explains how truck classes relate to weight ratings.

Permits for heavy loads

Loads that cannot reasonably be divided, such as a large machine or a structural beam, can move above the legal limits with oversize or overweight permits from each state on the route. Permits set routes, times and sometimes escort requirements. Divisible loads, such as gravel or pallets of goods, generally have to be brought within the limits instead.

Exemptions and allowances

Federal rules allow some extra weight for certain equipment. Idle reduction technology, such as an APU, can be exempted up to 550 pounds where states apply the allowance, and some states require proof the unit works. Other allowances exist for specific fuel types and equipment. Check how the states on your route apply them before relying on them.

Weighing your truck

Certified truck scales are found at many truck stops. A scale ticket shows the weight on each axle group, so you can adjust before you leave. Our guide to truck axle scales explains how to weigh, read the ticket and adjust. For typical empty weights of tractors and trailers, see how much does a semi truck weigh.

Weight and the electrical side

Air suspension, onboard scales and some weight-related sensors depend on the truck's electrical and air systems. An onboard scale that reads wrong because of a sensor or wiring fault can lead you to load wrong. Our truck battery guide covers the electrical basics. To confirm a truck's exact model and ratings when buying, use the semi truck VIN decoder and read the certification label.

Weight limits by equipment type

Different equipment runs into weight limits in different ways:

• Dry vans and reefers often hit the gross limit with dense freight such as beverages, paper or canned goods, even when the trailer is not full.
• Flatbeds and step decks carry steel, lumber and machinery, where axle limits and the bridge formula often matter as much as the gross limit.
• Tankers carry liquids that are dense and must be loaded to the right level to stay legal and stable.
• Dump trucks often run on state roads with their own limits, and many use extra axles to carry more.
• Box trucks are limited first by their GVWR, which is often reached before the box is full with heavy freight.
• Oversize and heavy haul loads move by permit, with route and time restrictions.

Fines and enforcement

States enforce weight limits at fixed scales, with portable scales and with weigh-in-motion sensors that flag trucks for inspection. Fines are usually based on how far over the limit a truck is, and can increase sharply for larger overages. Being held at a scale until the load is fixed can cost more than the fine, once a missed delivery is counted. When a load is near the limit, weigh before entering the highway.

Weight on the bill of lading vs reality

The weight on a bill of lading or a load posting is not always right. Shippers sometimes estimate, and pallets can be heavier than listed. Because the driver and carrier are responsible on the road, weigh after loading whenever the load is near your limit. If the shipper overloaded the trailer, ask them to adjust the load or document the problem before you leave.

Weight and safety

Weight limits are about more than roads and bridges. A heavier truck needs more distance to stop, puts more heat into its brakes on long descents and is harder to control in a sudden maneuver. An overloaded axle also wears tires and suspension faster. Staying within limits protects the truck, the load and everyone else on the road.

How dispatch handles weight

Before a load reaches you, a dispatcher should check the stated weight against your truck's empty weight and payload limit, and flag loads that are close. On heavy freight, it helps to know your empty weight to the hundred pounds and your typical axle split. Share those numbers with your dispatcher so heavy loads are checked properly before you accept them.

Common weight mistakes

• Guessing the empty weight. Fuel, tools, chains and an APU add up. Weigh the truck as you actually run it.
• Ignoring the steer axle. A fifth wheel slid too far forward can overload the steer axle even when the gross is fine.
• Trusting the paperwork. Weigh when the stated weight is close to your limit.
• Forgetting fuel burn. A truck that is legal after a long run may have been over at the shipper with full tanks.
• Assuming every state is the same. Limits on state roads and permit rules differ.

Weighing as a habit

Owners who run heavy freight often weigh every heavy load, not just the ones that seem close. Over time, they learn how their truck splits weight between axles with different freight, and can set the tandem and fifth wheel quickly. The few dollars a scale ticket costs are small next to a fine, a held load or extra wear from running overweight.

Where we fit

We dispatch 26 ft box trucks and larger, including heavy freight on flatbeds, step decks, dump trucks, tankers and oversize equipment. Learn more about our dispatch service.