Furniture sold in a flat carton is not a conventional piece broken down for transport. It is designed the other way round, beginning with the box and working back to the object.
The carton is the first constraint
Freight is charged largely by volume, so the volume of the packed product determines a substantial share of the cost of getting it to a customer.
Designers therefore work to a target carton size, and the dimensions of the finished piece are adjusted so that its panels stack efficiently within it.
Pallet and container dimensions set the outer limits, since a carton that wastes space in a container carries that waste through the whole distribution chain.
Sheet materials dictate the joints
Most flat pack uses engineered panels rather than solid timber, because they are dimensionally stable, cheap and available in consistent large sheets.
Such panels hold a screw poorly along their edges, which rules out many traditional joints and pushes designers towards fittings that clamp panels together mechanically.
Cam locks, dowels and threaded inserts distribute load across a wider area of the panel, which is why the same small hardware appears across unrelated products.
Assembly sequence is part of the design
A piece has to be assemblable by one person with a single tool, in a domestic space, without clamps or a workbench.
That requirement constrains the order in which parts join, and designs are revised when a step proves impossible to perform alone.
Instructions are drawn rather than written so they work across languages, and the drawing style itself is tested for whether people follow it correctly.
Rigidity has to come from somewhere
Panel joints resist compression well but twist easily, so a cabinet assembled only from its main panels will rack under load.
A thin backing board fixed across the rear provides most of the resistance to that twisting, which is why leaving it off produces a piece that feels wrong.
Wall fixings serve the same purpose for tall units, transferring load into the structure of the room rather than relying on the furniture alone.
Cutting waste drives the shapes
Panels are cut from large sheets, and the layout of parts on a sheet determines how much material becomes offcut.
Dimensions are therefore chosen partly so that parts nest efficiently, which is one reason product sizes cluster around particular figures across the category.
The same logic governs how many distinct panel shapes a design uses, since fewer unique parts means simpler cutting, simpler packing and fewer things to misidentify during assembly.