WayhomartPut two wire racks side by side on unit price and the comparison is usually wrong. On a bulky product the real difference is how much cubic space each unit occupies: one unit at 0.09 m³ and one at 0.02 m³ do not differ by a little. They differ by roughly an order of magnitude in units per container.
This note is about one thing only: putting a welded fixed frame and a knock-down frame on the same basis.
The short version
Compare CBM per unit, not unit price. Unit price covers material and labour at the factory. Ocean freight, inland transport and storage are charged on volume (or weight, whichever is greater). Only the two together make a landed cost that can be compared.
Why a welded frame ships air
A three-tier wire rack, whether a shoe rack, storage rack or shelving unit, is an open frame on three or four sides. Most of the space it encloses is empty, but when the frame ships welded, the carton has to enclose all of it.
So what you pay for is not the weight of the wire. It is the external volume of the carton. The more rigid the welded structure, the less the carton can be compressed, and the worse that ratio gets.
The arithmetic: CBM per unit = carton volume ÷ units per carton
CBM per unit = (carton length × width × height) ÷ units per carton
Use the carton’s outside dimensions in metres, and count every unit inside, including inner packs. Four decimal places are enough for a comparison.
Worked example. The figures below are assumptions for illustration, not our measured or quoted data:
| Format | Carton outside | Units per carton | CBM per unit |
|---|---|---|---|
| Welded frame | 600 × 450 × 350 mm | 1 | 0.0945 m³ |
| KD flat-pack | 620 × 460 × 120 mm | 2 | 0.0171 m³ |
In this example the gap comes from the air inside the carton, not from the product getting lighter. Same wire weight, same material cost, and a different space occupied.
Nominal container volume versus usable volume
Use the same assumption on both sides, or one of them will be overstated:
| Container | Nominal internal volume (approx.) | What else has to be assumed |
|---|---|---|
| 20′ GP | 33 m³ | Stacking stability, door opening, pallets or none |
| 40′ HQ | 76 m³ | The same, plus the difference between the front and rear of the box |
Nominal volume is not loadable volume. Cartons deflect under load, stack height is limited by the door, and pallets eat roughly a tenth of the space. Nominal figures are fine for a relative comparison; they are not fine for concluding that a shipment will fit.
What knock-down costs you
KD is not free volume. It moves cost into three places:
- Joint rigidity. A knock-down frame is locked into one rigid body by tabs, clips or bolts. A poorly designed joint shows up as racking after assembly, the most common failure mode.
- Assembly time and tools. A structure that needs tools reads as a defect at retail. Tool-free assembly is the baseline for a retail SKU, and time should be counted in minutes, not in “follow the instructions”.
- Retail perception. Once assembled, the customer must see one finished product, not a kit. Seams, step-offs and the edge treatment of the finish are all judged here.
The three-tier KD wire shoe rack is an example of the structure: flat carton out, rigid three-tier frame after assembly, no tools. It also shows the boundary. The frame can be knocked down; the load path cannot.
When not to go knock-down
- The installation requires one rigid unit. For example a frame built into fitted cabinetry, where any movement is unacceptable.
- The target price cannot absorb the locking-tab tooling. A knock-down structure usually needs an extra stamping or forming tool; at low volume it never amortises.
- The carton cannot protect it. A flat-pack has different load points from a fixed frame; drop and vibration testing has to be redone rather than inherited.
The order of decisions should be: container loading and packaging first, structure second. Not the other way round.
Six questions to ask before quoting
- What are the carton dimensions, units per carton and gross weight in KD state? Those three numbers are what produce CBM per unit.
- Is the joint a locking tab, a clip or a bolt? Does it need tools, and how long does assembly take?
- Does it loosen after repeated assembly cycles? Display floors often require repeated assembly.
- How many units fit in a 40′ HQ when flat-packed? “About” is not an answer here.
- Which transport tests were run on the flat-pack? Drop, vibration and compression are different tests and do not substitute for each other.
- Who pays for the tooling change, and how is it charged? It lands directly on first-order cost.
Question 6 connects to the 11 inputs a dish rack RFQ needs.
Put four numbers in one table
When comparing suppliers, keep all four columns instead of one:
| Item | Supplier A | Supplier B |
|---|---|---|
| Unit price (FOB) | — | — |
| CBM per unit | — | — |
| Units per container (same container type) | — | — |
| Freight per unit = freight per container ÷ units per container | — | — |
The fourth row is the real competitor to the unit price. Often the supplier with the higher unit price has the lower freight per unit, and wins on the total. The reverse happens too: the cheaper unit price is paid for in container loading.
Where to go next
- How the structure is actually made: the process limits are under wire forming and welding.
- A full re-design story: converting a dish rack to knock-down covers the locking tabs and the rail joint.
- Which structures exist in the category: shelving and storage racks.
Volume is only part of the cost. What has to be compared is cost per unit landed, and its assumptions (trade term, destination port, container type) belong on the quotation.
