CBM, volumetric weight and how freight is charged
How to work out CBM from carton size, how air and courier turn volume into chargeable weight, how sea freight is charged, and how many cartons really fit in a container.
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In short
- CBM is length × width × height in metres, times the number of cartons; a 60 × 40 × 40 cm carton is 0.096 CBM.
- Air freight charges the greater of actual weight and volumetric weight, which is volume in cm³ divided by 6,000, or by 5,000 for many couriers.
- Sea freight in less-than-container loads is charged on the greater of cubic metres and tonnes, at 1 CBM to 1,000 kg.
- Maersk lists a 20 ft container at 33 m³, a 40 ft at 67 m³ and a 40 ft high cube at 76 m³, but boxes leave gaps, so count cartons rather than trusting volume.
- Measure the packed carton on the outside; one extra centimetre on each side adds about 5 percent to a 60 cm carton's volume.
Anyone who ships goods meets CBM sooner or later: on a supplier's quotation, a freight forwarder's rate sheet or an export document. It is a measure of space, and the reason it matters is that carriers sell space, not just weight. This page explains how it is worked out, how the same volume is turned into a charge by air, courier and sea, and why a container never holds as much as its volume suggests.
What CBM is
CBM stands for cubic metre, the volume of a box one metre long, one metre wide and one metre high. For a carton it is:
CBM = length × width × height (in metres) × number of cartons
If the measurements are in centimetres, multiply them together and divide by 1,000,000. A carton 60 cm long, 40 cm wide and 40 cm high has a volume of 60 × 40 × 40 = 96,000 cm³, which is 0.096 CBM. A consignment of 250 of them is 250 × 0.096 = 24 CBM.
The calculator accepts centimetres, millimetres, metres, inches and feet and converts them exactly, since an inch is by definition 2.54 cm and a foot is 30.48 cm. It also gives cubic feet, because many price lists in the United States quote them: one cubic metre is 35.3147 cubic feet, so 24 CBM is about 847.6 cubic feet.
Some sizes you will meet often:
| Carton (cm) | CBM each | Volumetric weight at 6,000 | At 5,000 |
|---|---|---|---|
| 40 × 30 × 30 | 0.036 | 6.0 kg | 7.2 kg |
| 50 × 30 × 30 | 0.045 | 7.5 kg | 9.0 kg |
| 60 × 40 × 40 | 0.096 | 16.0 kg | 19.2 kg |
| 100 × 50 × 50 | 0.250 | 41.7 kg | 50.0 kg |
Volumetric weight: how air and courier charge for space
An aircraft or a delivery van runs out of space before it runs out of capacity to carry weight when the cargo is light and bulky, so carriers charge for whichever is larger: what the parcel weighs, or the weight it would have if it were packed densely enough to fill its space. The second figure is the volumetric weight, and it is found by dividing the volume in cubic centimetres by a number the carrier states:
volumetric weight (kg) = length × width × height (cm) ÷ 6,000
Maersk's explanation of air cargo describes the 6,000 divisor as an industry standard set by the International Air Transport Association, and it corresponds to a density of 167 kg per cubic metre. Many express couriers use 5,000, which charges bulky parcels more. Your carrier's rate sheet states which divisor applies, and the calculator lets you choose between 6,000, 5,000 and 4,000.
The chargeable weight is then the greater of the actual weight and the volumetric weight. For the 60 × 40 × 40 cm carton above, the volumetric weight is 96,000 ÷ 6,000 = 16 kg. If the carton weighs 14 kg, the carrier charges for 16 kg. If it weighs 20 kg, it charges for 20. Over 250 cartons, the volumetric weight is 4,000 kg against an actual 3,500 kg, so the shipment is charged as 4,000 kg by air.
The practical lesson is that light, bulky goods cost more to send by air than their weight suggests, and that tighter packing is a saving. Trimming a carton from 60 × 40 × 40 to 55 × 40 × 40 cm cuts its volumetric weight from 16.0 to 14.7 kg.
Sea freight: CBM or tonnes
For a full container, sea freight is quoted per container and volume does not change the price. For goods that share a container with other people's, called less-than-container load or LCL, the charge is made on a "weight or measurement" basis: the greater of the cubic metres and the tonnes, at 1 CBM to 1,000 kg. Forwarders call that a revenue ton. A pallet of 2 CBM that weighs 800 kg is charged as 2 units, since the volume is the greater, while a 1 CBM crate of machine parts weighing 1,500 kg is charged as 1.5.
The break-even density is therefore 1,000 kg per cubic metre. Most mixed cargo is lighter than that, between roughly 200 and 500 kg per cubic metre, so volume decides the charge for most LCL shipments; dense goods such as tiles or bottled liquids are charged by weight. Tariffs vary, and some use a different conversion, so check your quotation.
How much fits in a container?
Maersk's specification for dry containers lists the volume of a 20 ft container at 33 m³, a 40 ft at 67 m³ and a 40 ft high cube at 76 m³, with these internal dimensions to the load line:
| Container | Length | Width | Height | Volume |
|---|---|---|---|---|
| 20 ft | 5,896 mm | 2,350 mm | 2,393 mm | 33 m³ |
| 40 ft | 12,032 mm | 2,350 mm | 2,393 mm | 67 m³ |
| 40 ft high cube | 12,032 mm | 2,350 mm | 2,697 mm | 76 m³ |
It is tempting to divide the shipment's CBM by these. The 250 cartons above are 24 CBM, and 24 ÷ 33 is 73 percent of a 20 ft, which looks like it fits. It does not. Boxes are not water. Along the 5,896 mm length of a 20 ft container only nine 60 cm cartons fit, leaving 49 cm unused; across the 2,350 mm width, five 40 cm cartons fit, leaving 35 cm; and up the 2,393 mm height, five fit, leaving 39 cm. That is 9 × 5 × 5 = 225 cartons, or 21.6 CBM, 65 percent of the container's volume, so 250 cartons need more than one 20 ft container.
The calculator does this count for you, trying the six ways of standing the carton and keeping the best. For 60 × 40 × 40 cm cartons it gives:
| Container | Cartons that fit | Containers for 250 cartons |
|---|---|---|
| 20 ft | 225 | 2 |
| 40 ft | 500 | 1 |
| 40 ft high cube | 600 | 1 |
This is a floor rather than a ceiling. Mixing orientations can sometimes fit a few more, and a real load also loses space to pallets, bracing and the clearance needed to close the doors. On the other side, a heavy product reaches the container's weight limit before it fills the space, which the calculator does not check. Treat the count as a good first estimate and let your forwarder confirm it.
Measuring correctly
- Measure the packed carton, outside, including any strapping or pallet. Carriers charge for what they handle, not for the product inside.
- Use the greatest length, width and height, rounded up, if the carton bulges.
- Do not round every side down. An extra centimetre on each side of a 60 × 40 × 40 cm carton makes it 61 × 41 × 41, which is 0.1025 CBM instead of 0.096, a rise of 6.8 percent.
- Quote in the same unit as your carrier. If a rate is per cubic foot, use the cubic feet figure; if it is per kilogram by air, use volumetric weight.
What this tool assumes
- All cartons are the same size. For mixed cargo, add up the CBM of each size separately.
- Container volumes and internal dimensions are Maersk's published figures. Other lines and different box builds vary by a little, so use your carrier's figures for a firm quotation.
- The count of cartons that fit is straight stacking; it ignores weight limits, pallets and door clearance.
- Weight, volumetric weight and the choice of divisor follow your carrier's rate sheet, which governs any charge.
- Everything is worked out in your browser; nothing is sent anywhere.
If you need to convert other lengths and volumes, the Unit Converter handles them, and the Percentage Calculator is useful for working out how much a packing change saves.