Truck weight limit checker: federal axle and gross limits

The federal limits it checks

On the Interstate System, federal rules set four limits, and the lowest one that applies wins 343798:

• Gross: 80,000 lb for the whole vehicle.
• Single axle: 20,000 lb on any one axle, including any axle within a group.
• Tandem: 34,000 lb on two axles more than 40 and no more than 96 inches apart.
• Bridge Formula: a limit for every group of two or more consecutive axles 892873.

These weights include all tolerances, so 80,001 lb is over. A truck with a certified, working idle-reduction unit may carry up to 400 lb more, which the checker adds when you tick the box.

How the Bridge Formula works

The formula is W = 500 × (LN ÷ (N − 1) + 12N + 36), where L is the distance in feet between the outer axles of a group and N is the number of axles in it, rounded to the nearest 500 lb. The checker runs it on every group of consecutive axles, not just the whole truck, because a heavy group in the middle can be over even when the gross is fine. A few values:

Two consecutive tandems may carry 34,000 lb each if the first and last axle are 36 feet or more apart, even where the formula gives a little less. The whole vehicle never goes over 80,000 lb without a permit.

A worked example

EXAMPLE: a 5-axle tractor-semitrailer with 18 ft from steer to the first drive axle, a 52-inch drive tandem, 32 ft to the trailer tandem, and a 49-inch trailer tandem. At 12,000 lb on the steer and 17,000 lb on each other axle, it grosses 80,000 lb and passes every check. Shift the load back so the trailer tandem carries 36,000 lb and the drives 32,500, and the gross is still 80,000 lb, yet the truck is over: tandem, axles 4-5. Sliding the fifth wheel or the trailer tandem moves weight between groups, which is why scale tickets show each group.

Reading the result

Green and red axles

Every axle involved in a failed check turns red in the side view, so you can see whether the fix is moving weight forward, back, or off the truck. The list shows each limit with the actual weight and the allowed weight.

Gross is fine but a group is over

That's the most common surprise at a scale. Balance the load, adjust the tandem slide, or reduce weight. Running over on an axle group can be cited even when the gross is under 80,000 lb.

What it doesn't cover

State limits off the Interstate, grandfathered state limits, oversize and overweight permits, seasonal frost laws, posted bridges, and tire load limits are not modeled. Some states allow more on certain roads; others post lower limits. Check the state's DOT for the route, and get a permit before you move anything that can't be divided.

Getting the inputs right

Axle spacing

Measure from the center of one axle hub to the center of the next, on level ground, and round to the nearest quarter foot. On a sliding trailer tandem, measure where the slide is set for this load, since moving it changes both the spacing and the weight on each group. Write the numbers down once for each setup you run; they rarely change.

Axle weights from a scale ticket

A certified truck scale weighs the steer, the drive group and the trailer group separately. Enter a group's weight split evenly across its axles; for a tandem, half on each. The checker then tests the group, each axle and every Bridge Formula combination. Weigh loaded, with fuel and the driver on board, because that's how the truck will cross the next scale.

Before you book

Ask the broker the shipment weight and whether it's a scale weight or the shipper's estimate. Add it to your empty weight. If the total sits close to a limit, ask whether the shipper can load to a lower weight or how the pallets will be placed.

Box trucks and hotshots

For a 26 ft box truck, the GVWR is usually the limit that bites first, not the road limits. Many are rated at or under 26,000 lb, just below the 26,001 lb point where a CDL is required 199283. A hotshot pickup and gooseneck combination has its own ratings: the truck's GVWR, the trailer's GVWR, and the combined rating. Stay inside all of them and the road limits rarely matter. We dispatch 26 ft box trucks and up.

Why it matters for every load

An overweight ticket, a forced reload or a refused load costs more than any rate gain. Ask the weight before you confirm, check it against your truck's empty weight and ratings, and scale early in the trip. For heavier freight that needs permits, see our notes on oversize dispatch and the guide to heavy haul brokers. Before a heavy run, check your brakes with the brake adjustment limit checker, and see whether the load pays for the extra fuel with the load profitability calculator. More on the tools page, or apply for dispatch.