Guide · Weights and volume
CBM calculation for cartons: the formula, cm vs inches and rounding
CBM is the volume of a carton in cubic metres. In centimetres, multiply length x width x height and divide by 1,000,000, then multiply by the number of cartons. Errors come from inches read as centimetres, rounding each carton instead of the total, and mixed units.
The formula
CBM means cubic metres, also written m³ or cu m. Use the outer dimensions of the packed carton, not the product. A 60 x 40 x 30 cm carton is 72,000 cubic centimetres, which is 0.072 CBM, so 20 of them are 1.440 CBM. The packing list shows this figure per row and in total, and the same total feeds container planning.
Volume matters twice. Sea LCL freight is typically charged per cubic metre or per tonne, whichever is greater under the carrier's terms, and air freight converts volume to a volumetric weight with a divisor such as 6,000 or 5,000 cubic centimetres per kilogram, depending on the carrier. Check the quote rather than assume.
General information, not customs or legal advice. The measurement on a packing list is the shipper's declaration; a carrier may re-measure and charge on its own figure.
Calculate CBM in six steps
Measure the packed carton
Length, width and height of the outside of the carton, including any bulge, in one unit. Use the same orientation for every carton of a SKU.
Convert to centimetres
Inches x 2.54, millimetres / 10, metres x 100. So 24 x 16 x 12 in is 60.96 x 40.64 x 30.48 cm.
Multiply and divide
Length x width x height gives cubic centimetres. Divide by 1,000,000 for CBM per carton.
Multiply by the carton count
Row CBM is CBM per carton x cartons in the row. Keep full precision until the end.
Add the rows
Sum the rows, round the total once to three decimals, and compare it with the list's declared total and the booking.
Sanity-check against weight
A carton over 1 CBM is unusual, and gross kilograms per CBM far outside what the goods normally weigh points to a wrong dimension. See gross weight vs net weight.
Worked examples
Each row starts from the carton size as written on a list and ends at the row CBM.
| Carton size as written | In cm | CBM per carton | Cartons | Row CBM |
|---|---|---|---|---|
| 60 x 40 x 30 cm | 60 x 40 x 30 | 0.072 | 20 | 1.440 |
| 50 x 40 x 30 cm | 50 x 40 x 30 | 0.060 | 10 | 0.600 |
| 600 x 400 x 300 mm | 60 x 40 x 30 | 0.072 | 20 | 1.440 |
| 24 x 16 x 12 in | 60.96 x 40.64 x 30.48 | 0.075512 | 50 | 3.776 |
| 2.5 cu ft | n/a | 0.070792 | 40 | 2.832 |
| 24 x 16 x 12 read as cm (wrong) | 24 x 16 x 12 | 0.004608 | 50 | 0.230 |
Rounding and conversions
Round once, at the end. Rounding the inch carton above up to 0.08 first gives 50 x 0.08 = 4.00 CBM against the true 3.776, an overstatement of 0.224 CBM, about 6 percent. For other units, 1 CBM is about 35.3147 cubic feet.
Carriers may apply their own rounding or minimum charges. Show the true figure on the list and ask for the rule in the quote.
What goes wrong
- Inches read as centimetres. 24 x 16 x 12 typed as cm gives 0.004608 CBM per carton instead of 0.075512, about 16 times too small. The whole row, and the total, understate the volume.
- Rounding too early. Rounding per carton multiplies the error by the number of cartons.
- Product size instead of carton size. The packing adds volume. Only the outer carton dimensions give the space the carton takes.
- Mixed units in one list. Millimetres on some rows and centimetres on others, or a cubic-feet figure dropped into a CBM column. State the unit in the header; the packing list template for exporters does.
- A total that is not the sum. A row edited after the total was typed, so the declared CBM and the rows disagree.
How CargoSheet helps
When a row has a carton size but no CBM, CargoSheet computes it (length x width x height x cartons, in cm unless the list writes mm, in or m, with cubic feet converted), rounds once to three decimals and marks the row "CBM computed". It flags a carton over 1 CBM and compares the sum with the declared total, but cannot check a size against the real carton. Try the packing list to Excel converter. Free: 1 file per day, up to 10 pages, no account. Files over 10 pages are converted up to page 10 on the free allowance; a page code converts the whole file, up to 150 pages. See pricing.
Questions
- How do you calculate CBM for a carton?
- Multiply length x width x height in centimetres and divide by 1,000,000. A 60 x 40 x 30 cm carton is 0.072 CBM. Multiply by the number of cartons to get the row.
- How do you calculate CBM from inches?
- Convert each side to centimetres by multiplying by 2.54, or multiply the three sides in inches and the result by 0.0000163871. A 24 x 16 x 12 in carton is 4,608 cubic inches, which is 0.075512 CBM.
- What does CBM mean?
- Cubic metre, written CBM or m³. It is the usual volume unit for ocean freight, used for container planning and for LCL charges.
- Should CBM be rounded?
- Round the total, not each carton, and keep three decimals on the list. Some carriers apply their own rounding or minimum charges, which their quote should state.
- Are the carton dimensions the product size?
- No. Use the outside dimensions of the packed carton, including any bulge. Product dimensions understate the volume.
- How many CBM fit in a container?
- Roughly 33 CBM of internal volume in a 20 ft container, 67 in a 40 ft and 76 in a 40 ft high cube, before allowing for gaps between cartons and pallets. Weight can limit the load first; see container load plan from a packing list.
Check a packing list against its own totals
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