How to stack boxes on a pallet: what can go on top of what
Five rules for stacking boxes on a pallet or in a vehicle, a table of the load on the bottom box, and how strong your boxes need to be.
When you stack boxes on a pallet, the usual problem isn't fitting them, it's crushing them. The bottom box carries the weight of every layer above it; if it can't, the stack collapses on the road and the goods on top get damaged.
This guide covers the rules that decide what goes on top of what, and how to work out how strong the bottom box needs to be.
The load on the bottom box
When you stack identical boxes, the bottom one carries the number of layers above it times the box weight: six layers of 12 kg boxes put 5 × 12 = 60 kg on the bottom box.
| Box weight | 4 layers | 5 layers | 6 layers | 8 layers |
|---|---|---|---|---|
| 5 kg | 15 kg | 20 kg | 25 kg | 35 kg |
| 10 kg | 30 kg | 40 kg | 50 kg | 70 kg |
| 15 kg | 45 kg | 60 kg | 75 kg | 105 kg |
| 20 kg | 60 kg | 80 kg | 100 kg | 140 kg |
How strong do the boxes need to be?
Your packaging supplier gives a box's compression strength (BCT, box compression test) in kilograms or newtons. It's measured in a lab: dry, and over a short time. Humidity, time in storage and vibration on the road all reduce it, so the load is multiplied by a safety factor. Factors between 3 and 5 are common.
Example: six layers of 12 kg boxes. The bottom box carries 60 kg; if the pallet will sit in a warehouse for a few weeks, a factor of 4 means the box needs at least 240 kg of strength.
| Conditions | Factor | Strength needed |
|---|---|---|
| Short trip, dry conditions | × 3 | 180 kg |
| A few weeks in storage | × 4 | 240 kg |
| Humid conditions, cold storage or months in storage | × 5 | 300 kg |
1. Heavy at the bottom, light on top
Heavy boxes go at the bottom. That stops the boxes below being crushed and keeps the pallet's centre of gravity low; a pallet with a high centre of gravity tends to tip under braking and on bends.
If a pallet mixes weights, put light but weak boxes (empty cartons, foam, textiles) on top.
2. Wide bases under narrow ones
The box on top should sit fully on the one below. Put a wide box on a narrow one and its edges hang in the air, the load lands on the middle of the box, its weakest part, and it caves in.
The load planner applies this rule: a box only goes on top of another if it's fully supported underneath.
3. Column stacking or interlocked stacking?
In column stacking each layer sits exactly on top of the one below, corners over corners. Most of a box's strength is in its corners, so this is the layout that best preserves compression strength.
In interlocked (brick) stacking each layer is turned relative to the last. It holds the pallet together, but the corners no longer line up and the load the boxes can carry drops noticeably. For heavy loads, column stacking plus stretch wrap or edge protectors is usually the safer combination.
4. No overhang
A box hanging over the pallet edge carries its load on an unsupported wall and loses a large part of its strength. Overhang also makes neighbouring pallets rub against each other and makes the pallet measure bigger than it is.
If your boxes don't fit the pallet, see the box size table in the pallet guide; changing the box size is often cheaper than overhanging.
5. Loads that can't take weight, and pallets on pallets
Fragile goods, liquids, and boxes without a flat top or that can't take the weight should be marked non-stackable. In the load planner that means unticking the item's "Stackable" box: nothing goes on top of it.
To stack pallets, the lower pallet needs a flat, sturdy top, and the two layers together have to fit the vehicle's internal height (a container's door height). The truck and container guides give the maximum height per layer by vehicle type.
Frequently asked questions
- How many layers of boxes can you stack?
- It depends on the box's compression strength and weight. The load on the bottom box is (layers − 1) × box weight, and it shouldn't exceed the box's strength divided by a safety factor (usually 3 to 5). A box rated at 240 kg carries 60 kg at a factor of 4: six layers of 12 kg boxes.
- Where do heavy boxes go on a pallet?
- At the bottom. Heavy boxes on top crush the ones below and raise the pallet's centre of gravity, making it more likely to tip.
- Is column stacking or interlocked stacking better?
- Column stacking, for strength: box corners line up. Interlocked (brick) stacking holds the pallet together better but lowers the load the boxes can carry. Heavy loads use column stacking with stretch wrap.
- What is BCT?
- Box compression test: the highest load an empty box can take from above before it collapses. Packaging suppliers give a box's BCT in kilograms or newtons.
- Can pallets be stacked on top of each other?
- Yes, if the lower pallet has a flat, sturdy top, the load won't crush, and both layers together fit the vehicle's internal height. Weight matters too: the upper pallet adds to the load on the lower pallet's boxes.