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.

What is the Axle Weight & Load Distribution Calculator?

Distribute cargo weight across the drive and trailer (tandem) axle groups using cargo position along the trailer, add empty-truck axle weights, and check totals against US federal single, tandem, and gross limits. For dispatchers and load planners. It runs free in your browser on Gera Tools, with nothing uploaded.

Axle Weight & Load Distribution Calculator

Name: Axle Weight & Load Distribution Calculator
Creator: Gera Tools
License: https://creativecommons.org/licenses/by/4.0/

Get one useful tool a week

Like this tool? Enter your email and we'll send you one genuinely useful Gera tool a week — plus a link to come back to this one. No spam, one-click unsubscribe any time.

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.

Worked example

A truck with empty weights of 12,000 lb (steer), 15,000 lb (drive tandems), and 9,000 lb (trailer tandems) carries 40,000 lb of cargo centred at 60% toward the trailer:

Axle group	Empty weight	Cargo share	Loaded weight	Federal limit	Status
Steer (single)	12,000 lb	—	12,000 lb	20,000 lb	OK
Drive (tandem)	15,000 lb	16,000 lb	31,000 lb	34,000 lb	OK
Trailer (tandem)	9,000 lb	24,000 lb	33,000 lb	34,000 lb	OK
Gross	—	—	80,000 lb	80,000 lb	At limit

Shifting the load centre forward to 40% would produce: drive 24,000 lb + 15,000 = 39,000 lb — over the 34,000 lb tandem limit, even though gross stays at 80,000. This illustrates why cargo position matters as much as total weight.

How to fix an overweight axle

Drive axle over limit: Move cargo toward the trailer end (increase position %). Alternatively, slide the fifth wheel rearward to redistribute load from the drive to the trailer group.

Trailer axle over limit: Move cargo toward the drive end (decrease position %). Sliding the trailer tandems rearward increases the effective lever arm and shifts load from the trailer tandems back to the drive axles.

Gross over 80,000 lb: Split the load across two trips, obtain an overweight permit (state-issued, route-specific), or offload until the weight is legal.

The Federal Bridge Formula

The federal 80,000 lb gross limit assumes standard axle spacing. The Federal Bridge Formula is a tighter constraint: it limits the weight allowed on any group of consecutive axles based on the spacing between the outermost axles of that group. Tightly spaced axles (less than the standard 4-foot tandem spread) receive a lower weight allowance than 34,000 lb. Most standard 5-axle tractor-trailer configurations at proper spacing comply with both the per-axle limits and the Bridge Formula simultaneously.

The lever split used here is a planning approximation. Confirm against a certified scale before dispatch. State limits on non-Interstate roads can be lower than federal Interstate limits.