Ideally the boxes on a pallet cover the deck exactly. In practice the pattern leaves the outer boxes either hanging over the edge or sitting short of it, and both conditions cost something. The useful thing is that the cost is not vague: each one has a failure mode and a number attached.
What overhang actually does
A box that projects past the deck edge is the box that gets hit. It is hit by the doorway, by the racking upright, by the next pallet on the truck and by the fork of the truck that misjudges the turn. Because the overhanging part is unsupported, the impact goes into the unsupported panel rather than into the deck, and the panel is the weakest direction of a corrugated board. Overhang of more than about 20 mm is where most edge damage starts.
The stretch wrap problem
Wrap pulls the top of a load inwards. Where boxes overhang, that pull is applied to unsupported board and tends to fold the edge down rather than hold the load together. Packers compensate by adding wrap, which adds cost and does not fix the geometry. The correction is in the pattern, not in the film.
What underhang costs
Short of the deck edge, the load loses the support the pallet was providing and, more importantly, loses volume. The loss is not the gap itself; it is that the gap usually runs the length of one side and cannot be filled by anything except a smaller box. In fleet terms, underhang converts a 1200-wide deck into an 1100-wide deck for the whole life of the box.
Where the two trade against each other
The interesting case is the pattern that is slightly over on one axis and slightly under on the other. That is usually better than either extreme, because the overhang is distributed and the unsupported strip is narrow. Deciding it needs the actual pallet dimensions rather than the nominal ones, since a repaired pallet can be 15 mm out.
Deck boards and the gaps between them
A box that sits over a gap between deck boards behaves as if it is overhanging, even when it is well inside the footprint. Patterns that place a box corner over a gap are a recurring source of puncture on the base. Lining the deck with a sheet removes the problem at low cost and is worth doing wherever the base carries a point load.
What to ask a supplier to confirm
Three things: the maximum overhang the box will tolerate at the rated load, whether the rating assumes a lined deck, and what the recommended wrap tension is. A supplier who has actually tested the box will have all three. One who has not will answer with a general statement about board strength.
Measuring it on a real pallet
Put six boxes on a deck and measure the projection at each edge with a rule. Where it exceeds about 20 mm, expect edge damage on that axis. Where the boxes sit more than 30 mm inside the deck edge, the pattern is giving up volume that a different footprint would recover.
Do it with the pallets the lane actually uses rather than a good one from the front of the stack. Repaired pallets, and pallets from an open pool, vary by more than the tolerance most patterns allow, and the variation is always in the direction that causes trouble.
What we can do
We build PP corrugated turnover boxes with the base designed for the deck they will sit on, including the lined-deck case. Tell us the pallet formats and the part weight, and we will state the overhang limit and the wrap tension we recommend. The base design side of this is covered in how a box base carries a point load.