CBM (cubic metre) is calculated as length × width × height (in metres) × number of packages. A 60 × 40 × 40 cm carton measures 0.096 m³, and a hundred of them make 9.6 m³. Forwarders quote LCL rates on this number, shippers use it to pick a container size, and warehouse teams use it to plan stuffing. This guide covers the formula, unit conversions, a multi-SKU example and how to turn a CBM total into a container estimate.
The basic CBM formula
One cubic metre is a space of 1 m × 1 m × 1 m. For box-shaped packages (cartons, crates, loaded pallets) the volume is the product of the three outer dimensions. Always use outer dimensions, not the carton maker's inner dimensions, because what takes up container space is the outside of the package, including flaps, strapping and pallet overhang.
The steps are:
- Convert length, width and height to metres.
- Multiply them to get CBM per package.
- Multiply by the number of packages.
If your dimensions are in centimetres you can multiply them directly and divide by 1,000,000. For irregular items such as machines, coils or furniture, measure the smallest box that encloses the item; the space around it is effectively lost to other cargo. See the glossary entry for CBM for the basic definition.
CBM of a loaded pallet
For palletised cargo, measure the pallet and its load as one block. A 1200 × 1000 mm pallet with 1,350 mm of cargo on a 150 mm pallet stands 1,500 mm tall, so its volume is 1.2 × 1.0 × 1.5 = 1.8 m³. Ten such pallets take 18 m³, even though the cartons on them, if they exactly cover the pallet footprint, add up to only 16.2 m³. The 1.8 m³ difference is pallet space you still pay for and still lose inside the container.
Unit conversions: cm, mm, inches and cubic feet
Packaging data rarely arrives in one unit. Indonesian factories tend to write centimetres, engineering drawings use millimetres, and US buyers ask for inches or cubic feet. The table summarises the conversion factors used most often.
| Source unit | To metres | Example size | Volume per package |
|---|---|---|---|
| Centimetres (cm) | ÷ 100 | 60 × 40 × 40 cm | 0.096 m³ |
| Millimetres (mm) | ÷ 1,000 | 600 × 400 × 400 mm | 0.096 m³ |
| Inches (in) | × 0.0254 | 24 × 16 × 16 in | 0.1007 m³ |
| Cubic feet (ft³) | ÷ 35.3147 | 3.5556 ft³ | 0.1007 m³ |
Useful anchors: 1 inch = 25.4 mm, 1 foot = 304.8 mm and 1 m³ = 35.3147 ft³. A 24 × 16 × 16 inch carton holds 6,144 cubic inches; divided by 1,728 (cubic inches per cubic foot) that is 3.5556 ft³, or about 0.1007 m³. Fifty of those cartons come to roughly 5.03 m³ or 177.8 ft³. To avoid typing errors, run conversions through the Unit Converter.
Worked example: a multi-SKU shipment
A small furniture exporter in Jepara, Central Java, is preparing one shipment with three SKUs. The packing list shows:
| SKU | Carton size (cm) | CBM per carton | Quantity | Total CBM | Gross weight |
|---|---|---|---|---|---|
| A | 60 × 40 × 40 | 0.096 | 100 | 9.60 m³ | 1,800 kg (18 kg/ctn) |
| B | 50 × 40 × 30 | 0.060 | 150 | 9.00 m³ | 1,800 kg (12 kg/ctn) |
| C | 45 × 35 × 30 | 0.04725 | 80 | 3.78 m³ | 800 kg (10 kg/ctn) |
| Total | 330 | 22.38 m³ | 4,400 kg |
Look at SKU C: 0.45 × 0.35 × 0.30 = 0.04725 m³. Round that too early to 0.05 m³ and SKU C becomes 4.0 m³ instead of 3.78 m³. A small error per carton becomes a large one over thousands of cartons.
The 22.38 m³ total is about 790 ft³. At 4,400 kg the shipment is far below a 20ft container's payload, so it is limited by volume, not weight. You can repeat this calculation SKU by SKU in the CBM Calculator.
From CBM to a container estimate
A container's inner volume can never be filled 100%. There are always gaps along the walls, under the roof and at the doors, especially when carton sizes do not divide evenly into the inner dimensions. As a rule of thumb (not a standard), mixed cartons typically fill 80–90% of inner volume.
| Container | Inner volume | Practical 80–90% range | Max payload (typical) |
|---|---|---|---|
| 20GP | 33.2 m³ | 26.6–29.9 m³ | 28,250 kg |
| 40GP | 67.7 m³ | 54.2–60.9 m³ | 26,730 kg |
| 40HC | 76.4 m³ | 61.1–68.8 m³ | 26,540 kg |
In our example, 22.38 m³ is about 67% of a 20GP's inner volume and below the practical range of 26.6–29.9 m³. One 20ft container is enough, with room left for dunnage or a late addition to the order. Payload figures are typical values; always check the CSC plate of the actual unit. For a full comparison of the three types, read 20ft vs 40ft vs 40HC, and look up dimensions in Container Sizes.
Two caveats. First, total CBM only tells you whether the goods might fit; it does not prove the cartons can be stacked neatly. The real carton count depends on how many fit along each axis, covered in how many cartons fit in a container. Second, for palletised goods, count CBM per loaded pallet (including the 144–150 mm pallet base) and check floor positions with how many pallets fit in a container.
Rounding the right way
Rounding is the most common reason shippers and forwarders disagree on a CBM figure. Safe practice:
- Calculate at full precision, round at the end. Keep CBM per package to at least four decimals, then round the shipment total to two or three.
- Follow the tariff rules. Many LCL tariffs charge a minimum of 1 m³ and round up to the next 0.01 or 0.1 m³. That is a commercial rule, not a mathematical one; ask your forwarder.
- Round dimensions up, not down. A carton measuring 40.6 cm should be recorded as 41 cm, not 40 cm, because the CFS will re-measure and charge on actual size.
In the multi-SKU example, rounding CBM per carton to two decimals (0.10, 0.06, 0.05) gives 23.0 m³, 0.62 m³ more than the true figure. On an LCL rate charged per W/M, that excess turns straight into cost.
Common mistakes
- Using inner carton dimensions from the box maker's specification instead of outer ones.
- Forgetting pallet height. A timber pallet adds about 144–150 mm, and uneven stacks waste the space above them.
- Mixing units in one spreadsheet, such as length in centimetres and height in inches.
- Assuming 33.2 m³ can be filled completely. Plan with a fill factor, then verify with a real stacking pattern.
- Ignoring weight. Dense goods such as ceramics or steel reach payload long before the space is full. Check road limits as well: a heavy 20ft load often runs into truck limits before it reaches the container's payload.
- Not re-measuring production samples. Mass-produced cartons can bulge a few millimetres compared with the approved sample.
Calculate and plan your load
Start with the CBM Calculator for volume per SKU, then take the same data into the 3D load planner to see how the cartons stack inside the container, how much space is left and what the total weight is. Planner output is a simulation for planning purposes; it does not replace official weighing, VGM, or operator and carrier approval.