Choosing a container size looks like a simple question and it quietly decides your cost per item. The answer is not always the smaller box, and it is not always the bigger one. It depends on volume, weight and what else you might add to the order.
Here is how to work it out in a few steps.
Step 1: know the three sizes
Three types cover almost all furniture and building material shipments.
A 20 foot container offers roughly 33 cubic metres of internal volume. A 40 foot standard offers roughly 67 cubic metres. A 40 foot high cube is the same footprint as the standard with about a foot more height, giving roughly 76 cubic metres.
Usable volume is always less than the internal volume, because cartons do not fill a space perfectly. As a working assumption, plan on filling around 85 to 90 percent of the stated figure.
Step 2: calculate your actual volume
Ask each supplier for the carton dimensions and the number of units per carton. Multiply length by width by height in metres to get the cubic metres per carton, then multiply by the number of cartons.
Do this before production if you can, because carton sizes can sometimes be adjusted slightly to stack more efficiently, and a small change can add items to the load at no extra freight cost.
Step 3: check the weight as well
Every container has a payload limit, generally in the region of 21 to 26 tonnes depending on the type and the route. Furniture rarely reaches it, since furniture is bulky rather than heavy. Tiles, stone and metal do reach it quickly.
If you are shipping tiles or stone, weight will usually decide the container before volume does. A 20 foot container often reaches its weight limit while looking half empty, which surprises first time buyers.
Step 4: compare cost per cubic metre, not per container
This is the step that answers the question. A 40 foot container costs more than a 20 foot but not twice as much, and a 40 foot high cube usually costs only a little more than a 40 foot standard while carrying noticeably more volume.
Divide each quoted rate by the usable volume and compare the results. For furniture, the 40 foot high cube is very often the best value per cubic metre, which is why it is the standard choice for the trade.
Step 5: consider what else you could add
If your volume sits between sizes, the useful question is whether the gap can be filled profitably. Adding stock you will need anyway, bringing forward a second order, or consolidating goods from another supplier all turn empty space into value.
If you are ordering from more than one factory, consolidating everything at one point before loading is usually cheaper than shipping two part loads separately.
Step 6: know when a part load is right
Below a certain volume, shipping a shared container makes more sense. Less than container load is charged by volume with handling fees at both ends, and those fees do not shrink with a small shipment.
There is a crossover point, often somewhere around 13 to 15 cubic metres depending on the route and the season, where a full 20 foot container becomes cheaper in total than a part load. Ask your forwarder to quote both for your actual volume, since the answer moves with the market.
A simple decision guide
Under about 13 cubic metres, ask for a part load quotation and compare it with a full 20 foot. Between roughly 15 and 28 cubic metres, a 20 foot container is usually right. Between about 28 and 60 cubic metres, look at the 40 foot high cube and consider adding stock to fill it. Above 60 cubic metres, a 40 foot high cube or multiple containers, planned so each is loaded well.
For dense goods such as tiles and stone, run the weight calculation first and let it lead the decision.
Two things worth doing either way
Ask for a loading plan and photographs at three stages, empty, half loaded and fully loaded. It confirms the space was used well and records what went in.
And if you are shipping several room types or several destinations within one load, ask for loading in that order. Unloading in the sequence you need saves real time at the other end and costs nothing to arrange.
Work the numbers this way and the container size stops being guesswork. If you would like help calculating volume and planning a load out of Foshan, our team does this every week.