The calculation
Volume in cubic metres is the three dimensions multiplied, expressed in metres. A carton of 60 × 40 × 35 cm is 0.6 × 0.4 × 0.35 = 0.084 CBM. Multiply by the carton count for the shipment total: 120 cartons is 10.08 CBM. Rounding up is standard practice — forwarders bill the measured volume, and a shipment measured at 10.2 CBM is rarely billed as 10.08.
Container capacity in CBM
Container volumes are theoretical; usable space is lower because of pallets, loading gaps and door height:
- 20ft container: 33 CBM theoretical, about 28 CBM usable
- 40ft container: 67 CBM theoretical, about 58 CBM usable
- 40ft high cube: 76 CBM theoretical, about 68 CBM usable
- LCL (groupage): no minimum container, but usually a 1 CBM minimum charge
The 1 CBM = 1,000 kg convention
Sea freight compares volume and weight using a ratio of 1 CBM to 1,000 kg (one revenue tonne). Cargo denser than 1,000 kg per CBM is billed by weight; lighter cargo is billed by volume. Knowing which side of the line you are on tells you whether to optimise packaging size or packing density — and the answer changes the freight strategy entirely.
LCL or full container
As a rule of thumb: under 12 CBM, ship LCL; between 12 and 15 CBM, compare carefully — total cost, transit time and handling all favour a container sooner than the raw numbers suggest; above 15 CBM, a 20ft container is usually cheaper and much less prone to damage and delay. The container capacity figures above give you the carton counts behind those thresholds.
Cutting CBM without cutting product
Repacking is the cheapest freight saving available. Moving the same 120 cartons from 60 × 40 × 35 cm to 55 × 38 × 32 cm reduces volume from 10.08 to 8.02 CBM — a 20% saving at any rate per CBM. Ask the factory for the smallest carton that meets the drop test rather than the most convenient one.
CBM in air and parcel freight
Air freight uses volumetric kilograms (cm³ ÷ 6,000, or 5,000 for express), and parcel carriers use dimensional weight (in³ ÷ 139 or 166). The underlying idea is identical: light, bulky cargo is billed for the space it takes. The CBM calculator also returns cargo density so you can predict which method will apply.