What is the Federal Bridge Formula?

The Federal Bridge Formula (FBF) is a mathematical formula used to determine the maximum weight that can be carried on a group of two or more consecutive axles. The formula is: W = 500 × ((L×N)/(N-1) + 12×N + 36), where W is weight in pounds, L is distance between axles in feet, and N is the number of axles.

What are the standard federal weight limits for commercial trucks?

Standard federal weight limits are: Single Axle - 20,000 lbs, Tandem Axle - 34,000 lbs, Gross Vehicle Weight - 80,000 lbs, and Steer Axle - typically 12,000-20,000 lbs. However, many states have different limits and special provisions.

Do weight limits change during different seasons?

Yes, many jurisdictions implement seasonal weight restrictions, particularly during spring thaw periods. These restrictions can reduce allowable weights by 10-40% on certain roads to prevent damage during freeze-thaw cycles.

Are there special weight allowances for dump trucks?

Yes, many states offer special provisions for dump trucks and other construction vehicles. These can include higher weight limits, tolerance allowances, or exemptions from certain restrictions when operating within specified distances of construction sites.

Truck Weight Limits Calculator

Calculate legal weight limits for your truck configuration across all 50 US states, Canadian provinces, and federal regulations. Ensure compliance and maximize your payload capacity with jurisdiction-specific calculations.

Instant Calculations

All Axle Configurations

65 Jurisdictions Covered

Unified Weight Calculator

Build your truck configuration visually or use the detailed calculator - changes sync automatically

Weight Compliance Status

Compliant

Warning (>95%)

Overweight

Visual Truck Builder

Design your truck configuration by dragging and dropping axles

Truck Configuration

Truck Type

Wheelbase (inches)

Bridge Distance

22' 9"

Front axle to rearmost axle

GVWR

66,000 lbs

Truck Configuration

Drag axles from the palette below to position them on the truck (measurements in inches), or use Enter/Space to add axles

Scale: 1 pixel = 1 inch (12 pixels = 1 foot) - Drawing is to scale

Axle Configuration

Position (inches)

Axles

Weight (lbs)

Spacing:inches

Position (inches)

Axles

Weight (lbs)

Internal Axle Spacing (inches)

Standard: 56"

Axle Palette

Drag these axle types onto the truck above to add them to your configuration

Steer Axle

Max 2 axles

Front steering axle - can be single or dual steer with 20,000 lbs capacity per axle

Drive Axle

Max 3 axles

Powered driving axles - can be single, tandem, or tridem

Auxiliary Axle

Max 4 axles

Lift axles - drag before drives for pusher configuration (tags only allowed on straight trucks)

Trailer Axle

Max 4 axles

Trailer axles - can be single, tandem, tridem, or spread axles

How to Use

• Drag axle types from the palette to add them to the truck
• Drag existing axles on the truck to reposition them
• Use the spacing field between axles for precise positioning
• Adjust internal spacing for multi-axle groups (tandems, tridems)
• Set custom spacing between auxiliary and drive axles
• Use this configuration with the weight calculator above
• Reset to default tandem dump truck configuration anytime

Bridge Distance

The bridge distance is measured from the front axle to the rearmost axle (excluding auxiliary axles). For straight trucks, this is from the steer axle to the rearmost drive axle. For tractor-trailers, this is from the front axle on the tractor to the rearmost axle on the trailer. For multi-axle groups (tandem, tridem), it includes the full spacing to reach the actual rearmost axle. This measurement is used in federal bridge formula calculations for weight distribution across bridges.

Truck Type: straight

Total Axles: 3

Total Weight: 66,000 lbs

Understanding Weight Regulations

Federal Bridge Formula

The Federal Bridge Formula (FBF) calculates the maximum weight allowed on a group of two or more consecutive axles.

W = 500 × ((L×N)/(N-1) + 12×N + 36)

W = Maximum weight (lbs)
L = Distance between axles (ft)
N = Number of axles

Common Weight Limits

Single Axle:20,000 lbs
Tandem Axle:34,000 lbs
Gross Vehicle Weight:80,000 lbs
Steer Axle:12,000-20,000 lbs

* Standard federal limits. State regulations may vary.

State-Specific Regulations

While federal regulations provide a baseline, many states have their own weight limits and permit requirements:

Common Variations:

• Tolerance levels (typically 3-5%)
• Seasonal weight restrictions
• Special permits for overweight loads
• Grandfather rights for older vehicles

Examples by Jurisdiction:

• Michigan: Up to 164,000 lbs GVW
• Ontario: 63,500 kg (140,000 lbs) GVW
• Federal Interstate: 80,000 lbs standard
• Spring restrictions: 10-40% reductions

⚠️ Important Compliance Notes

• Always verify current regulations with state DOT
• Consider seasonal weight restrictions on certain roads
• Account for fuel weight when calculating payload
• Maintain proper weight distribution across all axles
• Keep detailed weight tickets and documentation

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