"How much can this box hold?" is one of the most common questions we hear — and one of the most important to answer correctly. An undersized box leads to crushed shipments. An oversized box wastes money and materials. Let's get it right.
Understanding Box Strength Ratings
Corrugated box strength is described by two primary metrics:
Edge Crush Test (ECT) Measures resistance to vertical stacking forces. This is the most relevant specification for boxes that will be stacked on pallets or in warehouses.
Bursting Strength (Mullen Test) Measures resistance to puncture from concentrated pressure. More relevant for rough handling and sharp-cornered contents.
Most modern boxes are specified by ECT, but both ratings may appear on the box certificate.
Maximum Weight by Box Type
Single-Wall Corrugated (Standard)
| ECT Rating | Max Content Weight | Typical Use |
|---|---|---|
| 23 ECT | Up to 20 lbs | Light retail items |
| 26 ECT | Up to 35 lbs | Books, small electronics |
| 29 ECT | Up to 50 lbs | Clothing, housewares |
| 32 ECT | Up to 65 lbs | General merchandise |
| 40 ECT | Up to 80 lbs | Heavy consumer goods |
| 44 ECT | Up to 95 lbs | Industrial parts |
Double-Wall Corrugated
| Construction | Max Content Weight | Typical Use |
|---|---|---|
| BC Double-Wall | Up to 120 lbs | Heavy industrial items |
| AC Double-Wall | Up to 180 lbs | Machine parts, dense materials |
Triple-Wall
| Construction | Max Content Weight | Typical Use |
|---|---|---|
| Standard Triple | Up to 300 lbs | Crate replacement |
| Heavy Triple | Up to 500 lbs | Heavy machinery, export |
Gaylord Boxes
| Type | Max Content Weight |
|---|---|
| 4-Wall Standard | Up to 1,000 lbs |
| 4-Wall Heavy-Duty | Up to 1,500 lbs |
| 5-Wall Standard | Up to 2,000 lbs |
| 5-Wall Heavy-Duty | Up to 2,500 lbs |
Factors That Reduce Capacity
These maximums assume ideal conditions. Real-world factors that reduce effective capacity:
Moisture: A box exposed to humidity loses 30–50% of its compression strength. This is the biggest capacity reducer in practice.
Stacking duration: Boxes under sustained load for weeks gradually lose compression strength through a process called "creep." Short-term capacity is higher than long-term.
Used condition: Previously used boxes have some reduction in original strength. Grade A retains ~90%, Grade B ~80%, Grade C ~65%.
Box size: Larger boxes have proportionally lower stacking strength relative to their size. A large box rated at 32 ECT has a lower safety margin than a small box at the same rating.
Temperature: High temperatures (above 90°F) soften the starch adhesives in corrugated board, reducing strength.
The Safety Factor
We recommend a 2:1 safety factor for all packaging applications. This means choosing a box rated for twice the weight you plan to put in it.
Example: If your product weighs 30 lbs, select a box rated for at least 60 lbs (32 ECT single-wall or higher).
This accounts for the various real-world capacity reducers listed above and provides a buffer for unexpected handling conditions during shipping.
When to Step Up to Double-Wall
- Product weight exceeds 65 lbs
- Products will be stacked 4+ high on pallets
- Contents have sharp edges that could puncture single-wall
- Boxes will be stored in uncontrolled environments (humidity, temperature)
- Products are high-value and damage is costly
The cost difference between single-wall and double-wall is typically 40–60%, but the protection improvement is dramatic. For high-value products, double-wall is almost always worth the investment.