What CBM means
CBM is cubic metres: length × width × height in metres. A carton of 50 × 40 × 30 cm is 0.5 × 0.4 × 0.3 = 0.06 m³. Shipping lines, freight forwarders and couriers all price partly on space, because a ship or plane fills up by volume as well as by weight.
Sea freight: weight or measurement (W/M)
For a shared container (LCL), forwarders charge per “revenue ton”: the larger of the volume in m³ and the weight in tonnes. 3 m³ weighing 800 kg is charged as 3; 2 m³ weighing 2.5 tonnes is charged as 2.5. Most also have a 1 m³ minimum.
Air and courier: volumetric weight
Airlines usually convert volume with a divisor of 6,000 (cm³ per kg), express couriers with 5,000. A 50 × 40 × 30 cm carton weighs 10 kg volumetric by air, 12 kg by courier — even if it is full of feathers. You pay on whichever is higher, actual or volumetric.
When a full container is cheaper
As a rule of thumb, once a shipment passes about 13–15 m³, a full 20-foot container (FCL) often costs about the same as LCL and is faster and safer, because nobody else’s cargo is handled with yours. Ask your forwarder for both prices.
Questions
How do I calculate CBM?
Multiply length × width × height in centimetres, divide by 1,000,000, then multiply by the number of cartons. 10 cartons of 50 × 40 × 30 cm = 0.6 m³.
How many CBM fit in a 20 ft container?
About 33 m³ inside, of which roughly 25–28 m³ is usable for cartons. A 40-foot holds about 67 m³ and a 40-foot high cube about 76 m³.
What is W/M in shipping?
Weight or measurement: for LCL sea freight you are charged on whichever is larger, the weight in tonnes or the volume in cubic metres.
Why is air freight divisor 6000 but courier 5000?
Air cargo tariffs (IATA) use 6,000 cm³ per kg; express couriers use a stricter 5,000, which makes light, bulky parcels chargeable at a higher weight.
Sources
Last checked 2026-11-11. Free to use; please check important details before you rely on them.