Axle weight calculator
Enter your empty axle weights, the cargo weight and where it sits, and where your tandems are slid. You get estimated steer, drive and trailer weights and how much a tandem slide moves.
Updated October 2026 · Free, no signup
Empty weights (from an empty scale ticket)
Positions
Estimated axle weights
- Steer / 20,000 lb
- 11,963 lb
- Drive tandem / 34,000 lb
- 24,863 lb
- Trailer tandem / 34,000 lb
- 31,675 lb
- Gross / 80,000 lb
- 68,500 lb
Sliding the trailer tandems 1 ft forward moves about 633 lb from the drives to the trailer tandem. Sliding them back does the opposite.
Estimate from static moments; a certified scale ticket is the only number that counts. Federal Interstate limits shown (23 CFR 658.17); check the Bridge Formula and your state.
Balanced at 68,500 lb gross. We send you loads with weights that fit your setup, and you confirm each one before it's booked.
Get loads that fit my truckHow it's calculated
The calculator uses static moments, the same math a scale house uses in reverse:
- Trailer tandem share = cargo x (cargo center behind kingpin / kingpin-to-tandem distance)
- Kingpin share = cargo - trailer tandem share
- Steer share = kingpin share x (fifth wheel distance ahead of the drives / tractor wheelbase)
- Drive share = kingpin share - steer share
- Each group = its empty weight + its share
Empty weights come from an empty scale ticket, axle group by axle group. The calculator then compares each group with the federal Interstate limits: 20,000 lb single axle, 34,000 lb tandem, 80,000 lb gross.
Source: 23 CFR 658.17 (FHWA) · checked 2026-10
Worked example
| EXAMPLE: 53 ft dry van, 42,000 lb load | |
|---|---|
| Empty: steer / drive / trailer | 11,000 / 8,500 / 7,000 lb |
| Cargo center behind kingpin | 23.5 ft |
| Kingpin to trailer tandem center | 40 ft |
| Trailer tandem gets | 24,675 lb of cargo, 31,675 lb total |
| Kingpin gets | 17,325 lb |
| Fifth wheel 1 ft ahead of drives, 18 ft wheelbase | steer +963 lb, drive +16,363 lb |
| Steer / drive / trailer | 11,963 / 24,863 / 31,675 lb |
| Gross | 68,500 lb |
Every group is under its limit. Load the same freight toward the nose and the drives climb; load it toward the doors and the trailer tandem goes over first.
What the result tells you
All green: the load is balanced for the federal limits. Amber on a group: move freight, slide the tandems or the fifth wheel, or take weight off. Sliding tandems forward puts more weight on the trailer tandem and less on the drives; sliding them back does the reverse.
Federal limits apply on the Interstate. States set limits on other roads, and the Bridge Formula can cut your gross below 80,000 lb on short setups; check it with the weight limit checker. Never run overweight to make a load work.
Dump trucks and straight trucks
Straight trucks work the same way with two supports: the steer and the rear group, with the body's load center between them. Dump bodies load heaviest over the rear, which is why tandem and tri-axle dumps reach their rear group limit well before their gross. Use a scale ticket for every material and pit until you know how your body loads.
Questions about this calculator
How do you calculate axle weight?
Treat the trailer as a beam resting on the kingpin and the trailer tandem. The tandem carries the cargo weight times its distance behind the kingpin, divided by the kingpin-to-tandem distance; the kingpin carries the rest. The kingpin load then splits between the steer and drives depending on where the fifth wheel sits. Add each axle group's empty weight.
How much weight moves when I slide my tandems?
It depends on the cargo weight and where it sits. With 42,000 lb centered about 23.5 ft behind the kingpin and the tandems at 40 ft, one foot of slide moves roughly 630 lb between the drives and the trailer tandem. The calculator shows the number for your load.
What are the legal axle weights for a semi?
On the Interstate System, 20,000 lb on a single axle, 34,000 lb on a tandem and 80,000 lb gross, subject to the Bridge Formula. A typical 5-axle tractor-trailer at 80,000 lb runs about 12,000 lb on the steer and 34,000 lb on each tandem. States set limits on other roads.
How do I get weight off my steer axle?
Slide the fifth wheel back toward the drive axles. That shifts kingpin weight from the steer to the drives. Keep enough on the steer for safe steering and within the tire and axle ratings.
Can I trust this instead of a scale?
No. It's an estimate for planning where to put the load and how to set the tandems. Real trucks have fuel levels, uneven loads and suspension effects the math doesn't see. Weigh on a certified scale and keep the ticket.
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