CBM — cubic metres — is the unit freight forwarders book and bill on, because most cargo runs out of space before it runs out of weight allowance. This calculator turns your carton dimensions and quantity into total CBM, then shows how that volume maps to containers and to air-freight chargeable weight.
How it works
Each dimension is converted to metres and multiplied, then scaled by quantity:
per-box CBM = (L × W × H, all in metres)
total CBM = per-box CBM × number of boxes
air volumetric weight (kg) = total CBM × 167 (1:6000 rule)The total CBM is then compared against usable container capacities — about 33 CBM for a 20ft, 67 CBM for a 40ft, and 76 CBM for a 40ft high cube — to estimate fill percentage.
Container fill reference
| Container type | Usable volume (approx.) | Max payload (approx.) |
|---|---|---|
| 20ft standard | 33 CBM | 28,000 kg |
| 40ft standard | 67 CBM | 28,800 kg |
| 40ft high cube | 76 CBM | 28,600 kg |
| 20ft reefer | 28 CBM | 27,000 kg |
Real loads typically reach 80–90% of these figures once packing gaps are accounted for. If your CBM fill is above 100% of a 20ft but below 50% of a 40ft, a 40ft is the standard choice — but check whether the weight limit is also a constraint, since dense goods like tiles or machinery can hit the payload limit long before the space limit.
Worked example: sea vs air decision
A carton measuring 60 × 40 × 30 cm is 0.072 CBM. A hundred of them total 7.2 CBM and weigh, for example, 800 kg actual.
- Sea freight: 7.2 CBM fills about 22% of a 20ft container. Typically shipped as LCL (less-than-container-load), billed per CBM.
- Air freight: Volumetric weight = 7.2 × 167 = 1,202 kg. Since 1,202 kg exceeds the actual weight of 800 kg, the airline bills on 1,202 kg — a significant premium. For light, bulky goods, sea freight is almost always cheaper per unit.
Now consider a dense shipment: 100 cartons weighing 80 kg each (8,000 kg total) in the same dimensions. Volumetric weight is still 1,202 kg, but actual weight is 8,000 kg — the airline bills on actual weight. Dense, high-value, or time-sensitive goods can tip the comparison toward air despite the higher cost per kg.
Practical tips
- Always quote CBM when requesting sea-freight rates. Forwarders need it to determine whether LCL or FCL pricing applies.
- For air freight, compute both actual and volumetric weight and present the higher figure to get an accurate quote.
- Dimension your cartons before they are packed. Measuring packed boxes is accurate; measuring product-spec sheets often misses the actual shipping carton size.
- Cubic packing efficiency matters: a 5 cm wasted gap per carton across 200 cartons adds a full CBM to your quote.