Carton dimensions decide the freight bill more often than weight does. An exporter who adds two centimetres to each side of a carton to make packing easier has just added about fourteen per cent to the volume, and on a full consignment that is a real number on the invoice. Nobody notices, because the weight has barely moved.
This page covers the two calculations underneath almost every quote you receive: cubic metres, and chargeable weight. They are not the same thing, and chargeable weight is not the same by sea as by air.
Calculating CBM
CBM stands for cubic metre. The formula is:
CBM = length × width × height, all in metres
If your dimensions are in centimetres, divide each by 100 first, or divide the product in cubic centimetres by 1,000,000. Both give the same answer.
Example one — a carton. A carton measuring 60 × 40 × 40 cm is 0.60 × 0.40 × 0.40 = 0.096 CBM. Twelve of them come to 12 × 0.096 = 1.152 CBM.
Example two — a pallet. A pallet with a footprint of 1.20 × 1.00 m, loaded to a total height of 1.45 m including the pallet itself, is 1.20 × 1.00 × 1.45 = 1.74 CBM.
Two rules people get wrong. Measure the outside of the packing, not the product. And measure a loaded pallet from the ground to the top of the highest carton, including any overhang. Carriers measure what they have to stow, not what you intended to send. Our CBM calculator handles mixed consignments.
Chargeable weight by sea: the weight or measure rule
For less than container load sea freight you are billed on revenue tons, also called freight tons. The rule is written W/M, for weight or measure: you pay on whichever is greater, one cubic metre or one tonne. The basis can vary by trade and carrier, so check the quote, but the one-to-one comparison is the common case.
Light cargo. A consignment of 3.2 CBM weighing 1,100 kg. That is 3.2 CBM against 1.1 tonne. Volume is greater, so you are billed on 3.2 revenue tons.
Dense cargo. A consignment of 1.8 CBM weighing 4,500 kg. That is 1.8 CBM against 4.5 tonnes. Weight is greater, so you are billed on 4.5 revenue tons — two and a half times what the volume alone would have suggested. Tiles, stone, machinery parts and chemicals in drums behave this way. Textiles, packaging, furniture and empty containers of any kind do not.
The crossover is at a density of one tonne per cubic metre. Below that you are billed on volume, above it on weight.
Chargeable weight by air: divide by 6000
Air freight uses a volumetric divisor. Take the volume in cubic centimetres, divide by 6000 to get kilogrammes, compare with the actual gross weight and pay on the higher figure.
Light cargo. Six cartons at 60 × 40 × 40 cm, gross 11 kg each. Volume is 96,000 cm³ per carton, 576,000 cm³ in total. Divided by 6000 that is 96 kg volumetric, against an actual gross of 66 kg. Chargeable weight is 96 kg.
Dense cargo. Four cartons at 40 × 30 × 30 cm, gross 10.5 kg each. Volume is 36,000 cm³ per carton, 144,000 cm³ in total. Divided by 6000 that is 24 kg volumetric, against an actual gross of 42 kg. Chargeable weight is 42 kg.
The air crossover point is about 167 kg per cubic metre — one cubic metre is 1,000,000 cm³, and 1,000,000 ÷ 6000 is roughly 166.7. Anything lighter than that per cubic metre is charged on volume. Note that express and courier operators commonly use a divisor of 5000, which makes the same box heavier on paper. More on how this feeds a quote on our air freight page.
| Mode | Chargeable weight rule | Crossover density |
|---|---|---|
| Sea LCL | Greater of CBM or tonnes, billed as revenue tons | 1,000 kg per CBM |
| Air | Greater of actual kg or cm³ ÷ 6000 | About 167 kg per CBM |
| Courier and express | Greater of actual kg or cm³ ÷ 5000 | 200 kg per CBM |
| Sea FCL | Flat rate per container, subject to the weight limit | Not applicable |
How much actually fits in a container
You will see internal capacity figures quoted — around 33 CBM for a 20ft, 67 for a 40ft, 76 for a 40ft high cube. Those are geometric volumes. You will not achieve them, because cartons do not tessellate perfectly, pallets waste floor space, and nothing loads to the roof against the door.
The figures worth planning against are usable:
| Container | Usable volume, after stow loss |
|---|---|
| 20ft standard | roughly 28 CBM |
| 40ft standard | roughly 58 CBM |
| 40ft high cube | roughly 68 CBM |
These are planning figures, not guarantees. Good carton sizes on a sensible floor plan can beat them; awkward sizes and mixed pallet heights fall short. Plan against these and ignore the geometric figure.
Volume is only one limit. Every container also has a maximum payload, and for heavy cargo that binds long before the space does. In India the road weight limit on the leg between your factory and the port often binds first, which is why a dense consignment can be stopped by trucking rules rather than by the ship. Confirm the payload limit for the actual container and the road route before you plan a load. Dense product reaches the weight limit with the box half empty, and no amount of stowage planning changes that.
The FCL and LCL crossover
On most trades, somewhere between 11 and 13 CBM a 20ft full container starts to cost less than the same cargo shipped LCL. Below that, LCL is usually cheaper. Above it, take the box.
The crossover is not fixed. It moves with:
- The LCL rate on that lane. When consolidation is competitive the crossover pushes upward, sometimes past 15 CBM. On thin lanes with few consolidators it falls.
- Destination charges. LCL cargo is deconsolidated at a container freight station, and the charges there are levied per CBM or per revenue ton. On some destinations these are high enough to move the crossover by several cubic metres on their own. Ask what they are before comparing.
- Density. Heavy cargo hits revenue tons faster than it fills the container, so dense product crosses over at a lower CBM figure than the headline range suggests.
- Handling risk. LCL cargo is loaded, unloaded and restacked alongside other people’s freight. For fragile goods the crossover is lower than pure arithmetic implies, because the damage risk is a real cost.
- Transit time. LCL waits for a consolidation to fill and often transships. FCL is usually faster and more predictable, which matters more than the rate on a tight delivery.
- Free time and detention. An FCL gives you the box at your premises with its own free days. That has value if you need time to unload — see our note on how those clocks run in ocean freight.
Why carton dimensions matter more than exporters expect
Take the 60 × 40 × 40 cm carton at 0.096 CBM. Add two centimetres to every side, to 62 × 42 × 42 cm, and it becomes 0.109 CBM. That is a 13.9 per cent increase in volume from a change nobody would notice on the shop floor.
On a 200-carton consignment: 19.2 CBM becomes 21.9 CBM. By LCL you are paying for roughly 2.7 extra revenue tons of nothing. By FCL, a load that fitted a 20ft with room to spare is now uncomfortably close to the usable limit.
The same logic works the other way. Carton sizes that divide cleanly into the pallet footprint, and pallet heights that let two tiers fit the container’s internal height, recover volume most exporters never realise they are losing. Do this arithmetic once, properly, before the next print run of cartons. Terms above are defined in our glossary.
Frequently asked questions
How do I calculate CBM for cartons of different sizes?
Calculate each size separately and add the totals. Ten cartons at 0.096 CBM and six at 0.15 CBM is 0.96 plus 0.90, so 1.86 CBM. Do not average the dimensions — averaging dimensions of different-shaped boxes will give you the wrong answer, sometimes badly.
Is CBM the same as chargeable weight?
No. CBM is a measurement of volume. Chargeable weight is what the carrier bills on, and it compares volume against weight under a rule that differs by mode. By sea LCL you are billed on the greater of CBM or tonnes. By air, volume is converted to a weight using the 6000 divisor and compared with the actual weight. Same cargo, two different billing bases.
Should I include the pallet in the CBM?
Yes. The carrier stows the pallet with the cargo, so its footprint and its height both count. Measure from the ground to the top of the load, and include any overhang, because that is the space actually occupied.
At what volume should I switch from LCL to a full container?
Roughly 11 to 13 CBM on most trades, but treat that as the point at which you should ask for both quotes rather than the point at which you should decide. Get an LCL quote with all destination charges shown and an FCL quote for a 20ft, on the same lane and the same week, and compare the landed totals. On some lanes the answer arrives well below 11 CBM, and on others not until 15.