CBM: the number every quote starts with
CBM stands for cubic metre, and it is simply the volume your cargo occupies: length times width times height, in metres. A carton that is 1.2 m by 0.8 m by 1.0 m is 0.96 CBM. Add up every carton or pallet and you have the total CBM of the shipment. Almost every freight quote, sea or air, LCL or courier, starts from this number, because volume is what fills a container or an aircraft hold.
Measure the outer dimensions, including the pallet and any packaging, because that is the space the carrier actually loses to your cargo. Round up, not down. A shipment measured optimistically at the desk becomes a re-measure and a corrected invoice at the terminal, and the corrected version is rarely in your favour.
CBM in one line
CBM is length times width times height in metres, the amount of space your cargo takes up. Measure the outside of the packed cartons or pallets, add them together, and round up. This single figure is the starting point for most sea and air freight quotes, because carriers sell space, and space is what your cargo consumes.
Chargeable weight: the greater of two numbers
Chargeable weight is the figure the carrier actually bills, and it is always the greater of two numbers: the real, scale weight of the cargo, and its volumetric weight, a weight worked out from the volume. If your cargo is dense, like machinery or tiles, the actual weight wins and you pay by weight. If it is light and bulky, like cushions or lampshades, the volumetric weight wins and you pay by space. You never get charged on the smaller of the two.
The trick is the conversion factor, the divisor that turns volume into a weight. It is different for sea and air, and knowing which one applies is what lets you predict the bill.
The air freight rule: 1 to 6000
Air freight uses a dimensional-weight rule set by IATA. You take the volume in cubic centimetres and divide by 6000 to get the volumetric weight in kilograms. Put another way, 6000 cubic centimetres of space is treated as one kilogram, so one full cubic metre of air cargo has a volumetric weight of about 167 kg. Express and courier services often use a smaller divisor, 5000, which makes bulky parcels cost even more.
- Volumetric weight (air) = length x width x height in cm, divided by 6000. The answer is in kilograms.
- 1 CBM of air cargo is about 167 kg of volumetric weight. If your actual weight per CBM is below that, you pay on volume, not scale weight.
- Express often uses 5000, not 6000. That raises the volumetric weight of light parcels, so a courier quote can be higher than airport-to-airport air freight for the same box.
167 kg per cubic metre in the air
Under the IATA 1:6000 rule, one cubic metre of air cargo carries a volumetric weight of roughly 167 kg. If your goods weigh less than that per cubic metre, the airline bills you on the volumetric figure, not the scale weight. This is why light, bulky air shipments feel so expensive: you are paying for the space, converted into kilograms at a fixed rate.
The sea LCL rule: weight or measure
Less-than-container-load sea freight, where your cargo shares a container with others, uses a different convention called weight or measure, often written W/M. The carrier compares the weight in tonnes against the volume in CBM and charges on whichever is greater, treating one CBM as roughly one tonne (1,000 kg). So for LCL, the rough rule is: if your cargo is under about 1,000 kg per CBM, you pay by volume; if it is denser, you pay by weight.
- LCL is billed on the greater of CBM or tonnes, with one CBM treated as about one tonne (the revenue ton).
- Under about 1,000 kg per CBM, volume wins. Most general cargo is lighter than this, so LCL is usually quoted per CBM.
- Full container load (FCL) is different. A full container is priced as a flat rate for the box, so once you fill a 20 or 40 foot container, CBM stops driving the price and utilisation is what matters.
This is why there is a crossover point where LCL stops making sense. As your volume grows, the per-CBM LCL cost climbs until a flat-rate full container is cheaper, even if you cannot quite fill it. Knowing your CBM is what tells you where that line is.
How to use this to pay less
Once you can calculate CBM and chargeable weight, you can influence both:
- Measure and pack tightly. Wasted space inside cartons is CBM you pay for. Right-sized boxes and efficient palletisation directly lower the volume you are billed on.
- Know your density. Work out your kilograms per CBM. It tells you immediately whether you will be charged on weight or volume, and therefore which lever, lighter packing or denser loading, actually helps.
- Find the LCL-to-FCL crossover. Above roughly 13 to 15 CBM, a full 20 foot container is often cheaper than LCL. Calculate it for your rate rather than guessing.
- Watch the air divisor. For air, confirm whether the quote uses 6000 or 5000, and for bulky goods compare a courier rate against true air freight, because the divisor can flip which is cheaper.
- Plan the load before you book. Modelling how cartons fit onto pallets and into a container turns CBM from a surprise on the invoice into a number you set on purpose.
The bottom line
Freight is priced on space as much as weight, and chargeable weight is simply the greater of what your cargo weighs and what its volume converts to. CBM, the cubic metres your goods occupy, is the number underneath every quote. In the air, volume converts at 6000 cubic centimetres per kilogram, about 167 kg per CBM, and express services use a harsher 5000. At sea in LCL, the carrier charges on the greater of one CBM or one tonne, so most general cargo is billed by volume until you have enough to justify a flat-rate full container. None of this is guesswork once you measure honestly and know your density. Do that, pack tight, and find your crossover point, and the quote stops surprising you, because you calculated it before the carrier did.