What are the US federal axle limits?

Federal limits on the Interstate are 20,000 lb on a single axle, 34,000 lb on a tandem axle group, and 80,000 lb gross vehicle weight. States may set lower limits on non-Interstate roads, so always confirm the route's posted limits.

How is cargo split between the axles?

Cargo load transfers to the two trailer support points by the lever (moment) rule based on its position. Cargo over the trailer tandems loads them fully; cargo forward shifts load onto the drive axles. The tool interpolates linearly between those points.

Why does the steer axle matter?

Steer axles have their own single-axle limit (commonly 12,000 to 20,000 lb depending on tyres) and need enough weight for steering control. Most cargo position changes affect the drive and trailer tandems, so this tool keeps steer at its tare value.

What is the Federal Bridge Formula?

It limits the weight on any group of consecutive axles based on the spacing between them, to protect bridges. A standard 5-axle tractor-trailer at proper spacing is allowed the full 80,000 lb; tight spacing reduces the allowance below that.

How do I fix an overweight tandem?

Slide the trailer tandems or the fifth wheel to shift load between the drive and trailer groups, or reposition the cargo. Moving the load centre forward shifts weight from the trailer tandems to the drive axles, and vice versa.

Axle Weight & Load Distribution Calculator

An overweight axle can mean a citation, an out-of-service order, and bridge damage liability, even when the gross weight is legal. This calculator splits cargo across the drive and trailer tandem groups by where the load sits, adds the empty-truck weights, and checks each group against the federal limits.

How it works

Cargo transfers to the two trailer support points (drive axles and trailer tandems) by the lever rule, where position runs 0% at the drive axles to 100% at the trailer tandems:

share to trailer tandems = position%       × cargo
share to drive axles     = (1 − position%) × cargo
drive total   = empty drive  + drive share
trailer total = empty trailer + trailer share
gross         = steer + drive total + trailer total

Each group is then compared with its limit: 20,000 lb single, 34,000 lb tandem, 80,000 lb gross.

Example

A truck with empty weights of 12,000 (steer), 15,000 (drive), 9,000 (trailer) carries 40,000 lb of cargo centred at 60% toward the trailer. Trailer gets 24,000, drive gets 16,000. Totals: drive 31,000 (ok), trailer 33,000 (ok), gross 80,000 (at limit). Shift cargo forward and the trailer eases while the drive climbs.

Notes

The lever split is a planning approximation of true axle reactions and assumes a standard tandem-to-tandem geometry. The Federal Bridge Formula and lower state or posted limits can bind before these federal maxima. Confirm against a certified scale before dispatch.