Understanding TI and HI
In warehouse operations, pallet stacking is defined by two fundamental metrics:
* TI (Tier): The number of cartons placed on a single layer of the pallet deck footprint.
* HI (High): The number of layers stacked vertically within allowable height limits.
Total Cartons = TI × HI. For example, a pallet with 8 cartons per layer stacked 5 layers high has a TI of 8 and HI of 5, holding 40 cartons total.
Column Stacking vs Interlocking Configurations
* Column Stacking (Aligned): Cartons are aligned corner-to-corner directly over the layer below. Because corrugated carton corners bear the majority (~60–70%) of vertical compressive load, column alignment maximizes structural compression resistance. However, unbanded columns have low inter-layer friction and require stretch-wrap containment to prevent layer shifting in transit.
* Interlocking Stacking (Pinwheel / Brickwork): Cartons are rotated on alternating layers to interlock the unit load. While interlocking increases unit load cohesion, packaging literature notes that placing corners over weaker center-panel spans noticeably reduces bottom-box compression resistance compared to aligned columns.
Pallet Overhang and Edge Support
Allowing cartons to overhang the perimeter of a wooden or plastic pallet deck removes direct support beneath the carton corners. In distribution environments, unsupported perimeter edges substantially degrade box stacking durability and leave cartons vulnerable to impact punctures from forklift tines and adjacent pallet loads.
Geometric Pallet Calculation vs Structural Load Engineering
Important distinction: FreightPlanHQ’s pallet calculator provides a geometric spatial optimization—calculating how many rectangular boxes fit across a 2D pallet footprint within target vertical height bounds. This geometric calculation does NOT establish that a load is structurally safe to ship.
Safe pallet shipment requires evaluating corrugated flute type (B, C, or double-wall), Edge Crush Test (ECT) ratings, environmental humidity degradation, stretch-film containment tension, and dynamic transit vibration (under standards such as ASTM D4169 or ISTA 3A). Shippers should perform physical load testing or packaging engineering reviews for fragile or heavy freight.