Improper weight distribution is one of the leading causes of transportation accidents. A container that looks perfectly packed can become a safety hazard if the weight isn't properly balanced. Understanding center of gravity, axle weight limits, and load securing is essential for anyone involved in container logistics.
This guide covers the critical aspects of weight distribution and load safety that every logistics professional should know.
The Stakes Are High: Improperly loaded containers can cause:
- Vehicle rollovers during turns
- Loss of steering control
- Crane accidents during loading/unloading
- Cargo damage from shifting
- Regulatory fines and shipment rejection
- Serious injuries or fatalities
Understanding Weight vs Volume Constraints
Every shipment is limited by two factors: weight capacity and volume capacity. Many logistics professionals focus only on filling the space, but weight limits are equally critical.
| Container Type | Max Gross Weight | Tare Weight | Max Payload | Internal Volume |
|---|---|---|---|---|
| 20' Standard | 30,480 kg | 2,280 kg | 28,200 kg | 33.2 m³ |
| 40' Standard | 30,480 kg | 3,750 kg | 26,730 kg | 67.7 m³ |
| 40' High Cube | 30,480 kg | 3,940 kg | 26,540 kg | 76.3 m³ |
Key Insight: The 40' container has LESS payload capacity than the 20' despite being twice the volume. ISO regulations limit max gross weight to 30,480 kg regardless of size, and the larger container has a heavier structure.
Weight-Limited vs Volume-Limited Shipments
| Cargo Type | Limiting Factor | Examples |
|---|---|---|
| Dense Cargo | Weight-limited | Steel, machinery, metals, liquids, marble |
| Light Cargo | Volume-limited | Furniture, textiles, plastic products, electronics packaging |
| Mixed Cargo | Check both constraints | Most real-world shipments |
The WV-Check Rule: Always check both Weight and Volume constraints before finalizing any load plan. Exceeding either limit creates safety and compliance issues.
Center of Gravity (COG) Principles
The center of gravity determines how stable a loaded container will be during transport. Poor COG placement leads to tipping, swaying, and loss of vehicle control.
Side View - Optimal Load Distribution
┌──────────────────────────────────────────┐
│ Light Light Light │
│ Items Items Items │
├──────────────────────────────────────────┤
│ ████ ████ ████ Light Light │
│ Heavy Heavy Heavy Items Items │
├────────────────────────────────────────── │
│ Floor (COG near center) │
└──────────────────────────────────────────┘
Front → Rear
↑
Ideal COG: 40-50% of container length
(slightly forward for road transport)
COG Placement Guidelines
| Axis | Optimal Position | Consequence of Imbalance |
|---|---|---|
| Longitudinal (Front-Rear) | 40-50% of container length | Too far forward: excessive front axle weight. Too far rear: steering problems, jackknifing |
| Lateral (Side-Side) | Centered (within 5% of centerline) | Tipping risk during turns, uneven tire wear |
| Vertical (Top-Bottom) | As low as possible | Higher COG increases rollover risk |
Golden Rules for COG:
- Heavy items go on the bottom - Never stack heavy on light
- Heavy items go forward - Weight over axles provides stability
- Balance side-to-side - Left and right weight should be within 5%
- Distribute evenly front-to-back - Avoid concentration at either end
Axle Weight Regulations
Beyond total container weight, road transport is governed by axle weight limits that vary by country and road type.
| Region | Max Axle Weight | Total Vehicle Weight | Notes |
|---|---|---|---|
| USA | 9,070 kg (20,000 lbs) per axle | 36,000 kg (80,000 lbs) | Federal Bridge Formula applies |
| European Union | 11,500 kg per axle | 40,000-44,000 kg | Varies by country |
| UK | 10,500 kg per axle | 44,000 kg | For 6-axle vehicles |
| Australia | Varies by road type | 42,500-68,000 kg | Higher limits on designated routes |
The Bridge Formula: In the US, the Federal Bridge Formula limits weight based on the distance between axles. This prevents concentrated weight that can damage bridges, even when total weight is within limits.
Floor Load Limits
Container floors have specific load ratings that must not be exceeded, especially with heavy point loads like machinery.
| Container Type | Floor Load Rating | Point Load Limit |
|---|---|---|
| Standard 20'/40' | 4,800 - 7,000 kg/m² | Spreader boards required for forklifts |
| Heavy Duty / Flat Rack | 10,000+ kg/m² | Designed for concentrated loads |
Protect the Floor:
- Use spreader boards or dunnage to distribute heavy point loads
- Never drive forklifts directly on container floors without protection
- Machinery should be placed on wooden beams or steel plates
Stackability and Crush Resistance
Not all cargo can support weight stacked on top. Understanding stackability is crucial for maximizing container utilization safely.
Vertical Stacking Considerations
┌─────────────┐ ← Max height constraint (container ceiling)
│ Pallet 3 │
│ (Light) │
├─────────────┤ ← Stack stability check
│ Pallet 2 │
│ (Medium) │
├─────────────┤ ← Crush resistance check
│ Pallet 1 │ (bottom layer must support weight above)
│ (Heavy) │
└─────────────┘ ← Container floor
Stacking Rules:
✓ Total stack height ≤ container height
✓ Bottom items rated for weight above
✓ Heavy items on bottom, light on top
✓ Fragile items never on bottom
Stackability Checklist
| Factor | Check | Action if Failed |
|---|---|---|
| Crush Resistance | Can bottom item support weight above? | Don't stack, or add structural support |
| Height Limit | Does stack exceed container height? | Reduce stack levels |
| Fragility | Is bottom item fragile? | Move to top of stack |
| Stability | Is top smaller than bottom? | Larger items on bottom for pyramid stability |
Load Securing Requirements
Properly securing cargo prevents shifting during transport, which can cause accidents and cargo damage.
Securing Methods
| Method | Best For | Key Considerations |
|---|---|---|
| Blocking | Preventing forward/backward movement | Use wooden bracing, airbags, or cargo bars |
| Bracing | Filling gaps, preventing sideways movement | Dunnage, inflatable bags, foam |
| Lashing | Securing individual heavy items | Straps rated for cargo weight |
| Friction Mats | Preventing sliding | Place between pallets and floor |
CTU Code Guidelines: The IMO/ILO/UNECE Code of Practice for Packing of Cargo Transport Units (CTU Code) provides international standards for cargo securing. Key requirements include:
- Cargo must withstand forces of 0.8g forward, 0.5g sideways, and 0.5g rearward
- Lashing must be rated for at least 1.5x the force it will experience
- All gaps over 150mm must be filled to prevent shifting
Mixed Load Optimization
Most real-world shipments contain items of varying weights and dimensions. Here's how to plan a mixed load safely:
Mixed Load Strategy
- Sort by weight: Separate heavy items (>500kg per unit) from light items
- Heavy items first: Place heavy items on the floor, toward the front 40% of container
- Stack light on heavy: Never the reverse
- Fill gaps: Use light items to fill spaces between heavy items
- Balance sides: Ensure left and right sides have similar weight
- Calculate COG: Verify center of gravity is in the safe zone
- Secure everything: Block, brace, and lash as needed
Mixed Load Example - 40' Container
┌──────────────────────────────────────────────────┐
│ Light Light Light Light │
│ Boxes Boxes Boxes Boxes │
├──────────────────────────────────────────────────┤
│ ████████ ████████ ████████ Light Light │
│ Heavy Heavy Heavy Items Items │
│ (800kg) (800kg) (800kg) │
├──────────────────────────────────────────────────┤
│ Container Floor │
└──────────────────────────────────────────────────┘
Front (40%) → Rear (60%)
Total Weight: Heavy = 2,400kg in front 40%
Light = distributed across remaining space
Result: COG at approximately 45% - STABLE
Automate Your Load Planning
LoadPlanner calculates optimal weight distribution, center of gravity, and load sequences automatically. Stop guessing and start shipping safely.
Try LoadPlanner FreeCommon Weight Distribution Mistakes
- Loading heaviest items at the rear - Causes steering problems and potential jackknifing
- Stacking heavy on fragile - Crushes bottom cargo
- Ignoring lateral balance - One side heavier than the other causes tipping
- Filling to maximum weight without COG check - Legal weight can still be unstable
- Not securing gaps - Cargo shifts during transport
- Exceeding floor load limits - Machinery punches through container floor
Pre-Shipment Safety Checklist
- Total weight is within container payload limit
- Weight distribution places COG in safe zone (40-50% from front)
- Left and right sides are balanced (within 5%)
- Heavy items are on the bottom and toward the front
- No fragile items are under heavy items
- All stacks are within height limits
- Floor load limits are not exceeded
- All cargo is blocked, braced, and lashed
- Gaps over 150mm are filled
- Axle weight limits will be satisfied during road transport
Key Takeaways
- Check both weight AND volume - Either can be the limiting factor
- Center of gravity should be 40-50% from the front, centered side-to-side, and as low as possible
- Heavy items go on the bottom - Never stack heavy on light
- Balance left and right - Keep weight difference under 5%
- Respect floor load limits - Use spreader boards for heavy point loads
- Secure all cargo - Block, brace, and lash to prevent shifting
- Know your axle limits - Total weight compliance doesn't guarantee axle compliance
Ship Safely, Every Time
LoadPlanner ensures every shipment is properly balanced and safely loaded. Our optimization considers weight distribution, stacking limits, and center of gravity automatically.
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