Container capacity is quoted in cubic metres, and almost nobody achieves the quoted figure. The gap between nominal volume and loadable volume is where freight budgets go wrong.
The numbers to work from
| Container | Internal dimensions (approx) | Nominal volume | Realistic loaded volume | Typical payload limit |
|---|---|---|---|---|
| 20ft standard | 5.90 × 2.35 × 2.39 m | ~33 m³ | 25–28 m³ | ~21–22 t |
| 40ft standard | 12.03 × 2.35 × 2.39 m | ~67 m³ | 55–60 m³ | ~26–27 t |
| 40ft high cube | 12.03 × 2.35 × 2.69 m | ~76 m³ | 62–68 m³ | ~26–27 t |
Payload limits vary by container, by shipping line and by road weight limits in the destination country — the figures above are orientation, and the actual limit should be confirmed for the specific booking.
Why the realistic figure is 15–20% below nominal
Four losses, none avoidable:
- Carton tiling. Boxes rarely divide neatly into the container width. A carton 400 mm wide leaves 350 mm unusable across a 2,350 mm interior, and that strip runs the whole length.
- Stack height. The last layer usually does not fit, leaving headroom that cannot be used.
- Door end. Space is left to close the doors and to secure the load.
- Pallets. If goods are palletised, the pallet itself occupies 140–150 mm of height per layer and the pallet footprint rarely tiles perfectly either.
Palletised cargo typically loses more volume than floor-loaded cargo but loads and unloads far faster and suffers less damage. Which is right depends on the destination's handling equipment — sending pallets to a warehouse with no forklift creates a problem rather than solving one.
Cubing out versus weighing out
A shipment reaches one of two limits first:
Cubes out — the container is full but well under the weight limit. Typical for light bulky goods: packaging materials, textiles, plastic products. Here, volume efficiency is what matters and carton dimensions are worth optimising.
Weighs out — the weight limit is reached with space left. Typical for dense goods: machined parts, ceramics, liquids, metal products. Here, volume optimisation gains nothing, and the useful lever is reducing packaging weight.
Knowing which case you are in changes what is worth spending effort on. Redesigning cartons to gain 3 m³ on a shipment that weighs out is wasted work.
One 40ft or two 20ft
A 40ft container costs meaningfully less than two 20ft containers on most lanes — often in the region of 20–40% less than double — while offering roughly double the volume. So on volume alone, the 40ft wins.
Three situations where two 20ft still make sense:
- Dense cargo. Two 20ft containers give roughly 42–44 t of combined payload against 26–27 t in one 40ft. For heavy goods this is decisive.
- Road weight limits at destination. Some markets restrict axle loads such that a fully-loaded 40ft cannot legally be hauled from the port.
- Two delivery addresses. Splitting at origin is cheaper than splitting at destination.
LCL and where it stops making sense
Below roughly 15 m³, less-than-container-load shipping is usually cheaper. Above that, the LCL rate per cubic metre plus destination charges frequently exceeds the cost of a full 20ft container — and a full container also avoids the consolidation and deconsolidation handling where most LCL damage occurs.
The comparison should include destination charges, which are where LCL costs are least visible at booking and most surprising on arrival.
Before booking
- Confirm carton external dimensions and gross weight from the factory, measured on a packed carton rather than calculated.
- Ask the factory or forwarder for a loading plan on the specific carton size before committing to a container type.
- Check the destination's road weight limit if the shipment is dense.
- Confirm whether the goods will be floor-loaded or palletised, since it changes usable volume by several cubic metres.