How to Calculate CBM for Shipping Cartons
CBM (cubic metre) is the volume of your shipment. Learn the L×W×H formula in metres and centimetres, how CBM sets sea freight and air chargeable weight, and how to work it out for a carton.
CBM stands for cubic metre — a measure of volume, not weight. It is the single number freight forwarders use to price a shipment, because a truck, a container and an aircraft hold a fixed volume, and how much of that volume your boxes take up is what you are paying for. One CBM is a cube 1 m × 1 m × 1 m, which is exactly 1,000,000 cm³ (35.31 cubic feet). If your carton measures 60 × 40 × 40 cm, its CBM is 0.096 — a little under a tenth of a cubic metre.
The CBM formula
For one box: CBM = length (m) × width (m) × height (m). For a shipment: add up the CBM of every carton. If you measure in centimetres, multiply L × W × H in cm, then divide by 1,000,000 (or move the decimal point six places left). The mistake that costs buyers money is mixing units — using centimetres for one dimension and metres for another, which shifts the result by a factor of 100.
| If you have | Formula | Example |
|---|---|---|
| One carton in cm | L × W × H ÷ 1,000,000 | 60 × 40 × 40 cm = 0.096 CBM |
| One carton in metres | L × W × H | 0.6 × 0.4 × 0.4 m = 0.096 CBM |
| A whole shipment | Sum of every carton's CBM | 500 cartons × 0.096 = 48 CBM |
| From cubic feet | CFT ÷ 35.31 | 10 CFT ≈ 0.283 CBM |
| From litres | Litres ÷ 1,000 | 50 L = 0.05 CBM |
Handy checks. Always confirm gross weight and carton dimensions on the packing list, not the product page.
Worked example (illustrative)
- A master carton measures 60 × 40 × 40 cm. In metres that is 0.6 × 0.4 × 0.4, so one carton = 0.096 CBM.
- You are shipping 500 cartons. Total volume = 500 × 0.096 = 48 CBM.
- A 20 ft container holds roughly 28–33 CBM of usable space depending on how tightly the cartons stack. 48 CBM therefore needs a 40 ft container (about 58–67 CBM usable), not a 20 ft.
- If each carton is 12 kg gross, the shipment weighs 6,000 kg gross — but sea freight is still priced on the 48 CBM unless the goods are very dense, in which case the forwarder may quote on the higher of weight or volume.
These figures are worked examples, not a quote; container capacities and rates vary by carrier and route, and the chargeable basis is always confirmed by your forwarder.
CBM, volumetric weight and when weight wins
Sea freight is essentially priced by volume (per CBM, or per container), so CBM is usually what matters. Air freight is priced by chargeable weight, which is the greater of actual gross weight and volumetric weight. The air industry standard divisor is 6,000 cm³ per kilogram, so volumetric weight (kg) = L × W × H (cm) ÷ 6,000. A large, light carton is billed on its volumetric weight; a small, heavy one on its actual weight. That is why lightweight packaging can be cheaper to fly than dense goods of the same volume, and why CBM alone does not tell you the full air cost.
Packing smarter cuts freight
Flat-packed cartons, nested mailers and folded bags all reduce CBM without changing the product. Consolidating mixed SKUs into one shipment with one packing list also avoids paying volume twice. Tell us the destination and product mix and we will flag which items pack flat.
Ask us to optimise packingFrequently asked questions
How do I calculate CBM?
Multiply the carton's length, width and height in metres. If you have centimetres, multiply L × W × H in cm and divide by 1,000,000. For a shipment, calculate one carton's CBM and multiply by the number of cartons, or add up every carton individually if sizes differ.
Is CBM the same as cubic metres?
Yes. CBM is the abbreviation for cubic metre, the volume of a cube 1 m × 1 m × 1 m. It equals 1,000,000 cm³, about 35.31 cubic feet, and 1,000 litres.
How many CBM fits in a container?
As a planning guide, a 20 ft dry container holds roughly 28–33 CBM of usable space and a 40 ft container roughly 58–67 CBM, depending on how tightly cartons stack and the palletised or loose loading method. Always confirm usable capacity with your forwarder before booking.
Does CBM apply to air freight too?
Air freight is billed on chargeable weight — the greater of actual gross weight and volumetric weight. Volumetric weight in kilograms is L × W × H in cm divided by 6,000. So CBM still matters for air, but it is converted into a volumetric weight rather than billed directly as volume.
Can packaging reduce my CBM?
Yes, often significantly. Flat-packed cartons, nested mailer boxes and folded bags take less volume than erected ones, and consolidating several SKUs into one shipment avoids shipping air. Choosing stackable carton sizes also fills a container more efficiently, which lowers the freight cost per unit.
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