Column vs Interlock Stacking
When to stack pallet layers in aligned columns for vertical strength versus interlocking them in a brick pattern for stability, and the measurable trade-off between the two.
Every palletised load is built one layer at a time, and you have two basic ways to arrange each layer relative to the one below: column stack or interlock. The choice is a genuine trade-off between vertical strength and lateral stability, and the right answer depends on your carton's compression strength and how the load will be handled.
Column stacking: aligned for strength
In a column stack, every carton sits directly on the carton below it, corners over corners, so the layers form continuous vertical columns. This matters because the corners and vertical edges of a box carry most of its compression strength, typically 60-70% for a regular slotted carton. Keeping corners aligned routes the weight of the upper layers straight down through the strongest part of each box.
- Strength: highest. A column-stacked load can carry significantly more before the bottom layer crushes.
- Stability: lower. With no overlap between layers, the stack behaves like loose blocks and can shear or topple under braking, cornering or a forklift jolt.
- Best for: strong, uniform cartons; heavy products; loads that will be stretch-wrapped and not double-stacked in transit.
Interlock stacking: woven for stability
In an interlock (or "brick") pattern, alternate layers are rotated, usually 90 or 180 degrees, so each carton bridges the seams of the layer beneath it, the way bricks bond in a wall. The layers tie together and resist sliding apart.
- Stability: highest. The woven pattern holds the load square through handling and transport.
- Strength: lower. Because corners no longer line up, weight lands on box faces and edges, so stacking strength can drop by roughly 40-50% versus a pure column stack.
- Best for: lighter loads, mixed cartons, anything handled roughly or shipped without full wrapping.
The trade-off at a glance
| Factor | Column stack | Interlock stack |
|---|---|---|
| Layer alignment | Corners over corners | Rotated, seams bridged |
| Compression strength | Highest (corners loaded) | ~40-50% lower |
| Lateral stability | Lower | Highest |
| Typical use | Strong, heavy, uniform cartons | Light, mixed, rough-handled loads |
| Stabiliser needed | Stretch wrap or strapping | Pattern self-stabilises |
The practical rule: column stack for vertical strength, interlock for stability, and stretch-wrap a column stack to recover the stability you traded away. Many shippers use a hybrid, column stack the bulk of the layers, then interlock the top one or two layers as a tie course to lock the cap in place.
How it affects your pallet count
Stacking pattern changes how a load behaves, but for a single carton size on a single pallet it usually does not change how many boxes fit per layer, both patterns place the same number of identical boxes on the deck, just oriented differently. Where it changes the count is at the edges: an interlock pattern only works cleanly when the layer can be rotated and still tile without overhang, which depends on how your box divides into the footprint.
Work it in order:
- Find the boxes-per-layer (the TI) and the layer count (the HI) for your carton and pallet in the TI-HI calculator, try the rotated pattern to confirm an interlock tiles without overhang.
- Build the full load, layers and total units in the pallet load calculator.
- If you cannot interlock without overhang, column stack and wrap instead, and confirm the footprint you are tiling onto against the standard pallet sizes reference, then preview the stack in the pallet calculator.