Truck Axle Weight Calculator

Estimate steer, drive and trailer tandem weights for a tractor-trailer from your empty scale weights, cargo weight and load position, checked against limits.

Units lb and feet kg and metres

Steer axle — empty rig (lb or kg)From a scale ticket of the tractor with the empty trailer hooked up.

Drive axles — empty rig (lb or kg)

Trailer axles — empty rig (lb or kg)

Cargo weight (lb or kg)

Cargo centre from the trailer nose (ft or m)For an even load filling the floor, use half the trailer length (26.5 ft for a 53′ trailer).

Kingpin set-back from the nose (ft or m)Usually about 3 ft (36 in).

Kingpin to trailer tandem centre (ft or m)Sliding the tandem back makes this longer.

Tractor wheelbase (steer axle to drive tandem centre) (ft or m)

Fifth wheel ahead of drive tandem centre (ft or m)Distance ahead of the drive tandem centre: 0 through the wheelbase. Behind-drive positions are outside this model.

Steer axle limit (lb or kg)Often the axle or tire rating. Enter 0 to skip any limit.

Drive tandem limit (lb or kg)US federal: 34,000 lb tandem, 20,000 lb single axle.

Trailer tandem limit (lb or kg)

Gross weight limit (lb or kg)US federal: 80,000 lb on the Interstate.

Being under 80,000 lb gross is not enough: each axle group has its own limit, and where the freight sits decides how its weight splits between the steer axle, the drives and the trailer tandem. Start from a scale ticket of your empty rig, add the cargo and where its centre sits, and this calculator works out each axle weight, flags any group over the limit and shows how much more you could load.

How to use this tool

Enter the steer, drive and trailer axle weights of the empty tractor-trailer from a scale ticket.
Enter the cargo weight and how far its centre is from the trailer nose.
Enter the kingpin set-back, the kingpin-to-tandem distance, the tractor wheelbase and the fifth-wheel position.
Check or change the axle limits for your route, then read the axle weights and margins.

Formula

Kingpin share = cargo × (S − d) ÷ S; steer share = kingpin share × f ÷ WB

d is the distance from the kingpin to the cargo centre, S the kingpin-to-trailer-tandem distance, WB the tractor wheelbase and f how far the fifth wheel sits ahead of the drive tandem centre. The rest of the cargo goes to the trailer tandem, and the rest of the kingpin share to the drives. Each share is added to the empty weights.

Example

An empty rig scales 11,000 / 13,000 / 9,000 lb. Load 40,000 lb with its centre 23 ft from the nose: 20 ft behind a kingpin set 3 ft back, halfway along a 40 ft span. Half the cargo, 20,000 lb, goes to the kingpin and half to the trailer tandem (29,000 lb). With the fifth wheel 1 ft ahead of the drives on a 20 ft wheelbase, the steer axle gains 1,000 lb (12,000 lb) and the drives 19,000 lb (32,000 lb). Gross is 73,000 lb.

Frequently asked questions

What are the US federal axle weight limits?

The usual federal Interstate limits are 20,000 lb single axle, 34,000 lb tandem and 80,000 lb gross, subject to bridge rules and exceptions. The default 12,000 lb steer entry is an illustrative rating, not a separate federal steer limit.

How do I move weight off the drive axles?

Slide the trailer tandem forward, which shortens the kingpin-to-tandem span and puts more of the load on the trailer axles, or move freight toward the doors. Sliding the fifth wheel only trades weight between the steer and drive axles.

How accurate is this estimate?

It is a static lever model with the cargo centre between kingpin and trailer tandem and fifth wheel between tractor axle groups. It omits suspension and frame effects, bridge calculations, tire ratings and route restrictions. Verify on a scale.

Sources

Last updated: 2026