CBM is the volume of your shipment in cubic meters. Multiply the carton length by the width by the height, then multiply by the number of cartons. One carton measuring 60 × 50 × 40 cm is 0.12 CBM; 100 of them are 12 CBM. Sea freight is usually charged per CBM, so this number decides a large part of your shipping bill.
The formula
In metric units: CBM = (length in cm × width in cm × height in cm) ÷ 1,000,000 × quantity.
In imperial units: CBM = (length in inches × width in inches × height in inches) ÷ 61,024 × quantity.
Always measure the outside of the carton, with packaging. The forwarder measures the packed carton, not the product inside. A product that is 58 cm long in a 60 cm carton ships at 60 cm.
Worked example: metric
100 cartons, each 60 × 50 × 40 cm, 12 kg each.
- One carton: 60 × 50 × 40 = 120,000 cm³. Divide by 1,000,000 = 0.12 CBM.
- Total volume: 0.12 × 100 = 12 CBM.
- Total weight: 12 kg × 100 = 1,200 kg.
Your shipment is 12 CBM and 1,200 kg. A forwarder quoting $55 per CBM would charge about 12 × $55 = $660 for the ocean freight (port charges and surcharges are separate).
Worked example: imperial
50 cartons, each 24 × 20 × 16 inches.
- One carton: 24 × 20 × 16 = 7,680 cubic inches. Divide by 61,024 = 0.126 CBM.
- Total volume: 0.126 × 50 = 6.29 CBM.
The same carton in both systems gives the same answer. 60 × 50 × 40 cm is 24 × 20 × 16 inches, near enough — 0.12 CBM per carton either way. If your two calculations disagree by more than a rounding error, one of the measurements is wrong.
The 1 CBM = 1,000 kg rule
Carriers compare your volume against your weight. The rule of thumb in sea freight is 1 CBM = 1,000 kg. Whichever is larger decides the chargeable amount.
- 12 CBM and 1,200 kg: 12 CBM equals 1.2 weight tonnes. Volume wins. You pay for 12 CBM.
- 12 CBM and 1,500 kg: 1,200 kg vs 1,500 kg — weight wins. Some lines charge the higher figure, so check the quote.
Light, bulky cargo pays by volume; dense, heavy cargo pays by weight. A shipment of pillows is mostly air and pays by CBM. A shipment of steel parts pays by weight.
Mixed carton sizes
Calculate each size separately, then add the CBM figures. A shipment of 60 cartons at 0.12 CBM and 40 cartons at 0.08 CBM is (60 × 0.12) + (40 × 0.08) = 7.2 + 3.2 = 10.4 CBM. Never average the carton sizes first — the average hides the real total.
Three mistakes that cost money
- Measuring the product instead of the carton. The forwarder charges the packed size. Add the packaging.
- Forgetting pallets. A pallet adds roughly 15 cm of height and its own footprint. A palletized shipment can measure 10–15% more than the cartons alone.
- Rounding down. Round each carton up to the nearest centimeter. A forwarder rounds up, and a 0.5 CBM surprise on a 12 CBM shipment is a 4% cost increase you did not budget for.