WayhomartThe same container, the same piece count, and two factories quote freight that differs. The gap is usually not the freight rate. It is how many cubic metres each piece takes.
There is one starting point: carton length times width times height, divided by the pack quantity. Once that number exists, the container type means something.
The short version
CBM per unit is carton volume divided by pack quantity. Container load is usable volume divided by CBM per unit, then discounted for stacking.
CBM per unit before container type
| Container | Nominal internal volume | When it fits |
|---|---|---|
| 20GP | about 33 m³ | trials, small mixed loads |
| 40GP | about 67 m³ | low cargo, a little cheaper |
| 40HQ | about 76 m³ | the default for volume cargo |
These are nominal figures for standard containers. Usable volume depends on the carrier and the box, and on door recess and any bracing added at loading. Nominal values are for a first estimate, not for a quotation.
The gap between 40GP and 40HQ is height, roughly 9 m³. Whether you can use those 9 m³ depends on how many layers your carton allows. Two cartons at 375 mm and 325 mm high give a different layer count in the same container, and that difference is bigger than changing container type.
Five real cartons, worked through
The five models below are from one category, with carton size and pack quantity taken from the product pages:
| Model | Carton | Pack qty | CBM per carton | CBM per unit | 40HQ cartons, nominal | Units, nominal | Units at 85% |
|---|---|---|---|---|---|---|---|
| WH-1001 | 510485375 mm | 3 | 0.0928 | 0.0309 | 819 | 2457 | 2088 |
| WH-1005 | 680485370 mm | 4 | 0.1220 | 0.0305 | 622 | 2488 | 2116 |
| WH-1011 | 530430340 mm | 3 | 0.0775 | 0.0258 | 980 | 2940 | 2499 |
| WH-1019 | 690430325 mm | 4 | 0.0964 | 0.0241 | 788 | 3152 | 2676 |
| WH-1030 | 530460355 mm | 4 | 0.0865 | 0.0216 | 878 | 3512 | 2984 |
Nominal units assume no gaps and exist only for comparison. The 85% column multiplies usable volume by 0.85, closer to what happens at loading with gaps and stacking loss. It is still an estimate, not a commitment.
Three things stand out:
- CBM per unit runs from 0.0216 to 0.0309, a spread of more than 40%, and close to a thousand pieces on one container. WH-1001 and WH-1011 are 515 mm and 560 mm long, 45 mm apart, yet differ by a fifth in CBM per unit. Carton shape and pack quantity do that, not product size.
- The largest carton, WH-1005 at 680 mm wide, is not the worst per unit, because it packs four. A big carton does not automatically eat volume; the divisor is the pack quantity.
- After the discount the range is 2088 to 2984 units. That band is what you can tell a customer before quoting. Anything tighter needs a loading photo or a pallet trial.
Reverse it: pieces first, container second
The more common question is how to ship two thousand pieces. Using the numbers above:
| Case | Arithmetic | Result |
|---|---|---|
| 2000 units of WH-1011 | 2000 × 0.0258 | about 51.6 m³ |
| 2000 units of WH-1001 | 2000 × 0.0309 | about 61.8 m³ |
| 2000 units of WH-1030 | 2000 × 0.0216 | about 43.2 m³ |
All three fit inside the nominal 67 m³ of a 40GP, with very different headroom. WH-1001 leaves about five cubic metres, not enough for a mixed load or a top-up. WH-1030 leaves more than twenty, room to add another item.
So the order is: total volume first, then whether the remaining space takes another SKU, then 40GP against 40HQ on freight. Book the container first and you usually discover the shortfall just before loading, turning two containers into three.
The cost of a wrong estimate is asymmetric. Undershoot and you add a container. Overshoot and you ship air or delay a top-up. Both cost money, and the first is more urgent.
Three variables, plus weight
| Variable | Effect | How to confirm |
|---|---|---|
| Stacking direction | height sets the layer count, one layer between carton heights | stack sample cartons, not drawings |
| Board strength | crushed bottom layers mean fewer layers than planned | ask for the board grade or a stacking test |
| Mixed loading | gaps between SKUs lower usable volume | with three SKUs or more, discount below 85% |
The fourth variable is weight. After volume, compare gross carton weight times carton count with the carrier’s payload limit, and take the smaller of the two.
Wire racks are not light. A container filled to its volume limit may already be at or over its payload. Discounting volume further solves nothing then; you ship fewer cartons or change container type.
Payload limits come from the carrier and the trade lane, so no figure is given here. Your forwarder will supply it with the quote.
A mixed load has a second cost that gets missed: the loading zones have to match the packing list order, or unloading means digging through the container. The configuration is set out in a two-SKU mixed container.
When this does not apply
- The product cannot lie flat, or the carton is not a cuboid, for example a 660 mm freestanding paper holder or a fully welded frame.
- The customer requires pallets, bracing or a walkway inside the container.
- Cargo ships dismantled, so carton count and finished piece count are not one to one.
- A mixed load is still being planned and the ratio is not fixed, which makes any number provisional.
Next steps
- Compare flat-pack and welded volume: KD versus welded wire racks.
- Two SKUs sharing a container: mixed container with two SKUs.
- Cartons with published dimensions: dish rack range.
- Have carton sizes and a target container: contact us to work the numbers.
