What is CBM, and how do you calculate it?
CBM means cubic metre. It is the space one carton fills. To calculate it, measure the carton in metres, then multiply length by width by height. A carton 60cm long, 40cm wide and 50cm tall is 0.6 by 0.4 by 0.5. That comes to 0.12 CBM.
Then multiply by how many cartons you have. Ten of those cartons is 1.2 CBM. That is the number your forwarder wants.
Measure the carton, not the goods inside it. Boxes have walls and padding, and you pay for the air too. This is the single most common mistake.
| Step | Example |
|---|---|
| Measure in metres | 0.6 x 0.4 x 0.5 |
| Multiply the three | 0.12 CBM per carton |
| Times the carton count | 0.12 x 10 = 1.2 CBM |
Why your forwarder charges by space and not by weight
Because a container runs out of room long before it runs out of weight. Pillows are light and fill a container fast. Car parts are heavy and take almost no space. So sea freight is normally priced per CBM, and your quote changes when the size changes.
Air freight works the other way. There you usually pay on weight, or on a volume figure if the goods are bulky and light.
Ask which one your quote uses before you agree. The same shipment can cost very different amounts under the two rules.
The mistake that makes your bill jump
Guessing the carton size from the product size. A supplier quotes you a CBM based on the goods, then packs them in bigger boxes with padding. Your real CBM is higher and the freight bill follows it. Ask for the packed carton measurements, in writing, before you pay.
Ask for three things: the size of one carton, how many pieces fit in it, and the total carton count. From those you can work out the CBM yourself in under a minute.
If a supplier will not give you carton measurements, that tells you something on its own. Real exporters know their box sizes without checking.
What to check before you agree a shipping price
Get the numbers in writing and do the sums yourself. None of this takes long and it is the cheapest hour you will spend on an order. A quote you cannot check is a quote you cannot compare with anyone else.
- Ask for the packed carton size in centimetres, not the product size.
- Ask how many pieces go in one carton, and how many cartons there are.
- Do the sum yourself. Length times width times height, in metres, times the carton count.
- Ask whether the quote is per CBM or per kilo, and get that in the same message.
- Check whether the price includes delivery to your port or to your door. They are not the same thing.