How each one works, in plain words
Air freight. Work out the volume of your cargo in cubic centimetres, then divide by 6,000. That gives you a number in kilograms, called the volume weight. You pay on that or on the real weight, whichever is higher.
Why 6,000? It is an old agreement about how much space one kilo of cargo is allowed to take up on an aircraft. It works out at one cubic metre being treated as 167 kg. Express and courier services often use 5,000 instead, which treats a cubic metre as 200 kg and makes light bulky parcels dearer.
Shared sea containers. The same idea, using tonnes and cubic metres, where one cubic metre is treated as one tonne. Whichever number is higher is what you pay on, and the answer is written in revenue tons.
Road. There is no single rule. Some hauliers charge on weight, some on the space taken, and some simply on the vehicle. This page shows you both numbers so you can ask the right question.
The mistake worth avoiding
Writing a sea chargeable weight in kilograms. A quote saying "chargeable weight 9.00 kg" for a container load of gloves means nine revenue tons. Everyone in the office knows that. No client does, and it makes the quotation look wrong.
What to do with the answer
If the space is what you are paying for, the cargo is light and bulky, and the money is in the packing. Can the cartons be smaller? Can anything be flat packed or nested? Is there air being shipped inside the boxes? On light cargo, a ten percent reduction in size is a ten percent reduction in the freight bill.
If the weight is what you are paying for, the cargo is dense, and repacking will not help. What helps there is the rate itself, the route, and whether a shared container is genuinely cheaper than a full one at your volume.
The crossover point matters. On sea, a shared container usually stops being sensible somewhere around 13 to 15 cubic metres, because at that point a full 20ft container often costs the same or less and comes with fewer handling charges. Ask for both prices before you assume.
Two habits
Measure the packed box, not the product. The carton, the pallet, the shrink wrap and the corner protectors are all being shipped, and the carrier measures the outside.
Get the measurements before you agree a price. A quotation given on estimated dimensions is a quotation that will change, and it will not change in your favour.