CBM Calculation and Volumetric Weight (Revenue Ton): Why LCL and Air Freight Aren't Priced by Weight Alone
Ship something light but bulky and the freight bill comes out far higher than the weight on the scale suggests. That is because carriers price by volume, not weight. Without knowing this rule, a quote can look impossible to explain.
What Is CBM?
CBM (Cubic Meter) is the volume a shipment occupies, expressed in cubic meters. The calculation is simple.
CBM = length (m) × width (m) × height (m)
For example, cargo measuring 1.2m long, 1.0m wide, and 1.0m high is 1.2 CBM. For multiple boxes, multiply one box's CBM by the quantity. If you measured in cm, divide by 100 to convert to meters first, then calculate.
Freight Is Charged on the Greater of Weight or Volume
For a carrier, cargo that takes up a lot of space is a cost just as much as heavy cargo. So they look at both weight and volume and price on the greater of the two. This basis differs between ocean and air.
Ocean LCL: Revenue Ton (R/T) Is the Greater of CBM or Weight
Small shipments that do not fill a whole container (LCL) are priced by revenue ton (R/T, Revenue Ton).
Revenue ton = the greater of CBM (volume ton) or weight ton (1,000kg = 1 ton)
- 1 CBM is treated as 1 ton (1,000kg).
- Compare the cargo's actual weight (weight ton) with its CBM (volume ton) and use the greater value as the revenue ton.
For example, cargo of 3 CBM weighing 1,500kg is charged at 3 R/T, the greater of volume ton 3 and weight ton 1.5. Conversely, heavy cargo of 1 CBM weighing 2,000kg comes to 2 R/T, since weight ton 2 is larger. Light cargo is driven by CBM, heavy cargo by weight.
Air: Volumetric Weight Is Divided by 6,000
Air uses a different basis. It converts volume into a volumetric weight. The IATA standard is as follows.
Air volumetric weight (kg) = length (cm) × width (cm) × height (cm) ÷ 6,000
- 1kg is treated as 6,000cm³.
- The greater of actual weight or volumetric weight becomes the chargeable weight.
For a box measuring 50cm on each side, the volumetric weight is 125,000 ÷ 6,000 ≈ 20.8kg. Even if the contents weigh just 5kg, the air freight is charged on 20.8kg. The bulkier the cargo, the greater the impact of volumetric weight in air freight.
Ocean and Air Basis Compared
| Category | Ocean LCL | Air |
|---|---|---|
| Volume basis | 1 CBM = 1,000kg | 6,000cm³ = 1kg |
| Unit of calculation | Revenue ton (R/T) | Chargeable weight (kg) |
| Charging method | Greater of CBM or weight ton | Greater of actual or volumetric weight |
Both methods share the same principle, "you pay on the greater of volume or weight," but the conversion basis and units differ. With just CBM and actual weight, you can check the freight under both bases with a calculator.
CBM Divides LCL from FCL
CBM is not only for calculating freight. It is also the basis for deciding whether to use a whole container (FCL) or split the load (LCL). Container capacities are roughly as follows.
| Container | Theoretical capacity | Practical loading |
|---|---|---|
| 20FT | About 33 CBM | About 25 to 28 CBM |
| 40FT | About 67 CBM | About 55 to 60 CBM |
As cargo CBM approaches the practical loading capacity of a 20FT, you reach the tipping point where FCL becomes more advantageous than LCL. The criteria and cost comparison for splitting LCL and FCL are covered in Ocean freight: LCL vs FCL. The air freight basis for bulky, light cargo continues in the Air freight guide.
This guide is for general information. Actual revenue ton and volumetric weight conversion bases can vary by carrier and airline policy, so confirm when requesting a quote.
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Frequently asked questions
How do I calculate CBM?
CBM is length (m) × width (m) × height (m). 1 CBM is one cubic meter (1m³). If you measured in cm, divide by 100 to convert to meters before multiplying, and for multiple boxes multiply one box's CBM by the quantity.
How is the ocean LCL revenue ton (R/T) set?
1 CBM is treated as 1 ton (1,000kg), and the greater of the cargo's CBM (volume ton) or actual weight ton is used as the revenue ton. Light cargo is driven by CBM, heavy cargo by weight.
Why is air volumetric weight divided by 6,000?
Because the IATA standard sets 1kg as 6,000cm³. The greater of the volumetric weight (length × width × height in cm, divided by 6,000) or the actual weight becomes the chargeable weight.
Why is the freight high when the cargo is light?
Carriers price on the greater of weight or volume. Light but bulky cargo is charged on volume (CBM or volumetric weight), so the freight exceeds what the scale weight would suggest.
