Stacking a pallet with different size boxes comes down to one core principle: heavy on the bottom, light on top, and no box hanging over the pallet edge. Get those basics right and you solve most stability and damage problems. The details below will help you build a load that stays intact through storage and transit.
Start With the Heaviest, Largest Boxes
Your first layer sets the foundation for everything above it. Place the heaviest and largest boxes directly on the pallet deck, centering their combined weight as evenly as possible. OSHA guidelines for load handling are explicit: set the heaviest loads on the bottom tier and the lightest on the top. This keeps the center of gravity low, which prevents tipping during forklift transport and makes the entire stack more resistant to shifting.
Arrange this bottom layer so boxes sit flush with the pallet edges or slightly inside them. Even a small overhang weakens the boxes underneath. Research on corrugated box strength found that a 1.5-inch overhang on two sides reduced a box’s compression strength by 49% compared to the same box sitting on a solid, fully supported surface. A half-inch overhang on one side is less dramatic, but the loss still adds up across multiple tiers. The takeaway: if a box doesn’t fit within the pallet footprint, it belongs on a different pallet or needs to be repositioned.
Build Each Layer as a Flat Platform
The goal for every tier is a level surface for the next tier to sit on. When your boxes are different heights, this takes some planning. Group boxes of similar height together on the same layer so the top of that tier is as flat as possible. If you have a few shorter boxes next to taller ones, fill the height gap before adding the next layer. Corrugated filler boards, foam blocks, or even sturdy cardboard scraps can bridge the difference. Products sometimes called “dunnage boards” are specifically designed for this: they combine corrugated material with a wood or rigid filler to create a level step between boxes of different heights.
Why does this matter so much? Corrugated boxes get their stacking strength from their corners and vertical edges. When a box sits on an uneven surface, the load presses unevenly on its walls, and the corners can’t do their job. You lose compression strength fast, and the boxes on the bottom start to buckle. A flat, fully supported base under each layer keeps that vertical column strength intact.
Fill Every Gap
Mixed-size loads almost always create voids: open spaces between boxes where nothing is supporting the load above. These gaps are where damage happens. Boxes bridge across empty space, sag under weight, and eventually crush or shift sideways during transit.
You have a few options for filling voids:
- Rigid void fillers: Lightweight blocks made from foam or corrugated material that fill cubic space without adding significant weight. They’re useful for large gaps between boxes of very different widths.
- Bulkhead panels: Flat panels that fill lengthwise or lateral voids, creating a wall between sections of the load.
- Dunnage boards: Rigid sheets placed between layers to distribute weight evenly across a tier that isn’t perfectly uniform. These are especially helpful for “step-down loads” where one section of a tier is taller than another.
- Cardboard or corrugated sheets: A simple, cheap option. Place a full-size corrugated sheet between each tier to spread weight across the entire layer below, even when box sizes vary.
The common mistake is thinking stretch wrap alone will hold everything together. Wrap helps, but it can’t compensate for a box that has nothing underneath one corner. Fill the voids first, then wrap.
Use a Pyramid Shape, Not a Tower
With mixed sizes, the most stable approach is a pyramid pattern: your largest, heaviest boxes form a wide base, and each tier gets progressively smaller and lighter as you go up. This naturally keeps the center of gravity low and centered. If you have medium boxes that are heavier than your large boxes, prioritize weight over size for the bottom layer, then arrange lighter, larger boxes around them to fill the footprint.
Avoid the temptation to alternate large and small layers or to place a wide, heavy box on top of a narrow one. Every time a box overhangs the one below it, you create an unsupported edge that weakens the load. Think of each box as needing full contact with whatever is beneath it, whether that’s another box, a filler, or the pallet deck itself.
Interlock or Column Stack?
When all boxes are the same size, many warehouses use an interlocking pattern where each layer is rotated 90 degrees from the one below, like bricks in a wall. This improves lateral stability. With mixed sizes, interlocking is harder to pull off cleanly, and it actually comes with a trade-off: the Fibre Box Association notes that interlocking stacking patterns compromise the corner support that gives corrugated boxes their strength. Boxes are strongest when their corners line up vertically in a straight column from top to bottom.
For mixed-size loads, column stacking (keeping corners aligned vertically within each group of same-size boxes) preserves more box strength. You compensate for the reduced lateral stability by using stretch wrap, strapping, or both. If you can arrange a few layers of identically sized boxes, stack those in columns. Where box sizes change between tiers, a corrugated slip sheet between layers adds friction and keeps things from sliding.
Secure the Finished Load
Once you’ve built your stack, it needs to be unitized into a single, rigid block. Stretch wrap is the standard tool. Wrap from the base up, anchoring the first few passes around the pallet itself so the load and pallet move as one unit. For mixed-size loads, extra passes around the middle tiers help because that’s typically where the load profile changes and shifting is most likely.
If your load has sharp transitions in size (a tier of small boxes sitting on a tier of much larger ones), corner protectors make a real difference. These are L-shaped strips of reinforced paperboard or plastic that sit on the vertical edges of the load. They spread strap tension across a wider area, prevent strap bite from cutting into box corners, and effectively “square off” an irregular load so the wrap or strapping pulls evenly. They also improve column strength for the boxes they contact.
For heavy loads or long-distance shipping, combine stretch wrap with horizontal or vertical strapping. The strapping locks the load to the pallet, while the wrap prevents individual boxes from shifting between the straps.
Watch Your Stack Height
OSHA requires that stacked cargo and pallets “provide stability against sliding and collapse” but doesn’t set a single universal height limit. Your practical limit depends on the strength of the bottom boxes, the weight of the load, and how level your stack is. A good rule of thumb: if you can’t keep the load’s center of gravity within the footprint of the pallet at every tier, you’re too high. Most standard pallets (48 by 40 inches) are safely stacked to about 60 inches of product height, but weaker boxes or uneven loads should stay shorter.
Pay attention to how long the load will sit in storage. Corrugated boxes lose compression strength over time, especially in humid environments. A stack that looks stable on day one can start to lean or crush after a few weeks if the bottom boxes are carrying too much weight relative to their rating. For long-term storage, err on the side of fewer tiers and stronger bottom layers.