Axle Weight Calculator
Calculate truck load distribution, verify DOT compliance, and avoid overweight fines.
Truck & Load Details
Distance from the center of the Steer Axle to the center of the Drive Axle group.
Please enter a valid wheelbase.
Distance from the center of the Drive Axle group to the Load's Center of Gravity. Positive values move forward towards the cab.
Please enter a valid distance.
Total weight of the cargo being loaded.
Please enter a valid payload weight.
Weight on front axle without load.
Weight on rear axles without load.
Legal limit (Default: 12,000 lbs).
Legal limit (Default: 34,000 lbs).
Total Gross Vehicle Weight
0 lbs
Within Limits
New Steer Axle Weight
0 lbs
—
New Drive Axle Weight
0 lbs
—
Payload Distribution
0% Front
(Amount of load on steer)
How it's calculated: We use the moment formula.
Weight Added to Steer = (Payload × Distance to Load COG) ÷ Wheelbase.
The remaining payload weight is supported by the Drive Axles.
Detailed Weight Breakdown
| Component | Steer Axle | Drive Axle | Total |
|---|---|---|---|
| Empty (Tare) Weight | 0 lbs | 0 lbs | 0 lbs |
| Payload Added | 0 lbs | 0 lbs | 0 lbs |
| Final Weight | 0 lbs | 0 lbs | 0 lbs |
| Legal Limit | 12,000 lbs | 34,000 lbs | — |
Axle Weight vs. Legal Limits
What is an Axle Weight Calculator?
An axle weight calculator is a critical tool for logistics professionals, truck drivers, and fleet managers designed to determine how a specific payload affects the weight distribution across a vehicle's axles. Unlike a simple gross weight check, an axle weight calculator breaks down the total load to ensure that neither the steer axle nor the drive axles exceed legal road limits.
Every commercial vehicle has a Gross Vehicle Weight Rating (GVWR) and specific axle weight limits mandated by the Department of Transportation (DOT). Exceeding these limits leads to hefty fines, increased wear on the vehicle, and safety hazards. This calculator helps you plan load placement accurately before you even hit the scales.
Axle Weight Calculator Formula and Explanation
The mathematics behind an axle weight calculator rely on the principles of physics known as "moments." A moment is the turning effect of a force around a pivot point. In trucking, the rear drive axle acts as the pivot point for calculating how much weight is transferred to the front steer axle.
The core formula used in this calculator is:
Weight Added to Steer = (Payload × Distance from Rear Axle to Load Center) ÷ Wheelbase
Once the weight added to the steer axle is found, the remainder of the payload is assigned to the drive axle.
| Variable | Meaning | Unit |
|---|---|---|
| Wheelbase (WB) | Distance between the center of the steer axle and the center of the drive axle group. | Inches |
| Load Center (d) | Distance from the center of the drive axle to the center of gravity (COG) of the load. | Inches |
| Payload (P) | Total weight of the cargo. | Lbs |
| Tare Weight | The weight of the truck when empty (fuel and driver included). | Lbs |
Practical Examples of Load Distribution
Example 1: Standard Freight Loading
Imagine a truck with a 250-inch wheelbase. The driver loads 40,000 lbs of cargo. The center of gravity of this load is placed 30 inches forward of the drive axles.
- Wheelbase: 250 inches
- Payload: 40,000 lbs
- Load Position: 30 inches forward of drive axle
Calculation:
Weight added to Steer = (40,000 × 30) / 250 = 4,800 lbs.
Weight added to Drive = 40,000 – 4,800 = 35,200 lbs.
Example 2: Sliding the Fifth Wheel
An axle weight calculator is also used to simulate sliding a fifth wheel. If you move the fifth wheel forward, you are essentially moving the load's center of gravity forward relative to the drive axles, transferring more weight to the steer axle. If a driver is overweight on the drives by 1,000 lbs, they can use the calculator to determine how many inches the load needs to move forward to shift that 1,000 lbs to the steers.
How to Use This Axle Weight Calculator
- Enter Wheelbase: Input the distance in inches between your steer axle hub and the center of your drive axle group.
- Define Load Position: Input how far forward (in inches) the center of your load is from the drive axles. If the load is centered directly over the drives, this is 0.
- Input Weights: Enter the total payload weight and your truck's empty (tare) weights for both steer and drive axles.
- Set Limits: Adjust the default DOT limits (12,000 lbs Steer / 34,000 lbs Drive) if your state or permit allows for different values.
- Analyze Results: The calculator will instantly show your new total weights and highlight any violations in red.
Key Factors That Affect Axle Weight Results
Several variables can drastically change your axle weight calculator results and real-world compliance.
- Fuel Weight: Diesel fuel weighs approximately 7 lbs per gallon. A full 200-gallon tank adds 1,400 lbs, mostly to the steer axle depending on tank placement.
- Bridge Law: Even if your axle weights are legal, the Federal Bridge Gross Weight Formula dictates the maximum weight based on the spacing between groups of axles to protect bridges.
- Sliding Tandems: On a trailer, sliding the tandem axles forward shifts weight from the drive axles to the trailer axles. Sliding them back does the reverse.
- Kingpin Setting: The position of the kingpin affects the turning radius and the weight distribution between the tractor and the trailer.
- Dunnage and Gear: Chains, tarps, straps, and headache racks add weight that is often overlooked in basic calculations but counts toward the gross weight.
- Auxiliary Power Units (APUs): Many states allow a 400-550 lb exemption for APUs, meaning your legal limit might be higher than the standard 80,000 lbs gross.
Frequently Asked Questions (FAQ)
What is the legal weight limit for a steer axle?
In the United States, the federal standard is typically 12,000 lbs for the steer axle, though tires rated for higher weights can sometimes allow for up to 20,000 lbs depending on the state and equipment.
How does sliding the fifth wheel affect axle weight?
Sliding the fifth wheel forward transfers weight from the drive axles to the steer axle. Sliding it backward transfers weight from the steer axle to the drive axles.
Can I use this for a spread axle trailer?
This specific calculator focuses on the tractor's steer and drive distribution. For spread axles, you would treat the trailer group separately, often allowing up to 20,000 lbs per single axle (40,000 lbs total) in many states.
Why is my scale ticket different from the calculator?
Real-world factors like uneven ground, suspension air pressure, fuel slosh, and inaccurate measurement of the load's center of gravity can cause slight variances.
What is the "Bridge Formula"?
The Federal Bridge Formula restricts the weight on any group of axles based on the distance between them and the number of axles, preventing concentrated weight that could damage bridges.
How much weight does sliding tandems shift?
A general rule of thumb is that sliding trailer tandems one hole shifts approximately 250 to 500 lbs, depending on the hole spacing and trailer length.
What happens if I am overweight on an axle?
If you are overweight at a weigh station, you may be issued a citation, forced to shift the load or slide axles to become legal, or in severe cases, placed out of service until the load is reduced.
Does this calculator account for permit loads?
You can use this calculator for permit loads by manually adjusting the "Limit" fields to match the higher weight allowances granted by your permit.
Related Tools and Internal Resources
- Gross Vehicle Weight Calculator – Calculate the total combined weight of your tractor, trailer, and load.
- Federal Bridge Law Calculator – Check if your axle spacing meets federal bridge formula requirements.
- Trucking Fuel Cost Estimator – Estimate trip costs based on weight and fuel efficiency.
- Truck Payload Capacity Guide – Determine the maximum cargo weight for different truck classes.
- DOT Compliance Checklist – Ensure your vehicle meets all Department of Transportation safety standards.
- Heavy Haul Route Planner – Plan routes that accommodate overweight or oversize loads.