CBM Explained: How to Calculate Volume, Volumetric Weight and Container Fit
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Short answer: CBM is the volume of your shipment in cubic metres — length × width × height in metres, per carton, times the number of cartons. Carriers then compare your actual weight with your volumetric weight (dimensions ÷ a divisor) and charge the higher one as chargeable weight. Use the <a href="/cbm-calculator">CBM Calculator</a> to run any carton size, divisor and container.
Worked example: 100 cartons, 60 × 40 × 40 cm, 20 kg each
One carton is 60 × 40 × 40 cm = 96,000 cubic centimetres, or 0.096 CBM. One hundred cartons are 9.6 CBM in total. Actual weight is 100 × 20 kg = 2,000 kg. Volumetric weight at the IATA air divisor of /6000 is 96,000 ÷ 6,000 = 16 kg per carton, or 1,600 kg in total. Chargeable weight is the higher of the two: 2,000 kg, so this shipment is charged on actual weight, not volume.
Flip the numbers and the answer flips too: the same cartons at 10 kg each would weigh 1,000 kg actually but 1,600 kg volumetrically, so the carrier would charge 1,600 kg. Light, bulky goods are almost always charged volumetrically — which is why shippers who only weigh their cartons get surprised by air-freight invoices.
Which divisor does your carrier use?
Air freight commonly uses /6000 under IATA rules. Couriers and express carriers often use /5000. Some carriers use /4000. The divisor is not a detail: the same 60 × 40 × 40 cm carton is 16 kg volumetrically at /6000, 19.2 kg at /5000 and 24 kg at /4000. Always confirm the divisor in your carrier's or forwarder's terms before quoting a customer, and use the calculator's divisor selector to compare all three on the same shipment.
Container fit is an estimate, not a packing plan: about 33 CBM in a 20ft container, about 67 CBM in a 40ft container and about 76 CBM in a 40ft high-cube. The 9.6 CBM example above fits in a single 20ft container at about 29% of its usable volume — but real loadable volume is lower once pallets, carton shapes, stacking limits and loading gaps are counted, so never book a container on a raw CBM figure alone.
What CBM does not tell you
CBM and chargeable weight do not produce a freight price. Rates depend on route, carrier, service level, fuel surcharges and the shipment's nature, and this guide deliberately does not invent rates. Use the CBM and chargeable weight from the calculator to request quotes from forwarders on a like-for-like basis — same volume, same chargeable weight, same divisor — and the quotes you compare will actually be comparable. For dangerous goods, oversized cargo or palletised loads, the forwarder's own measurement rules override any calculator.
FAQs
How do I calculate CBM?
Multiply length × width × height in metres for one carton, then multiply by the number of cartons. In centimetres: length × width × height ÷ 1,000,000 = CBM per carton.
What is volumetric weight?
A carrier's charge for light, bulky freight: length × width × height in centimetres ÷ a divisor. Air freight commonly uses /6000, couriers often use /5000, and some carriers use /4000.
What is chargeable weight?
The weight your freight is billed on: whichever is higher, actual weight or volumetric weight. If your cartons are heavy for their size you pay on actual weight; if they are light and bulky you pay on volumetric weight.
How many CBM fit in a 20ft container?
About 33 CBM of usable volume, versus about 67 CBM in a 40ft container and about 76 CBM in a 40ft high-cube. Real capacity is lower with pallets and irregular cartons.
Does this calculator give me a shipping price?
No. Freight rates depend on route, carrier and service level and are not estimated here. Use the CBM and chargeable weight to get comparable quotes from forwarders.