Checking a packing list before you book
Most of the time this figure is needed because a packing list has arrived and somebody has to sign off on it. The supplier has declared a total CBM, a consolidator is about to quote against it, and the number on the list is either right or it is about to cost money.
Enter each carton size on its own line, with the unit it was measured in. The page gives you the volume of one carton, the volume of each line and the shipment total, in cubic metres and in CFT, and prints the substitution underneath so you can check it against your own arithmetic rather than take it on trust.
Lines are added, never averaged. That matters more on a consolidation than anywhere else, because a consolidation is by definition several sizes at once, and an averaged figure can be out by half a cubic metre without looking obviously wrong.
Behind the form each measurement is held as an exact fraction rather than a decimal approximation, so 40 × 30 × 25 cm × 10 comes out as exactly 0.3 m³ — not 0.30000000000000004, which is what ordinary machine arithmetic produces for that particular sum.
CBM and CFT: the same shipment, two units
Freight paperwork here moves between two units constantly. A forwarder quotes LCL per cubic metre, while a packing list, a warehouse note or a trucking rate is as likely to be in CFT. They measure the same thing and the conversion is fixed: one cubic metre is 35.3147 CFT, and one CFT is 0.0283 m³.
CFT and ft³ are not two units. CFT is just the abbreviation that stuck on invoices and packing lists, and ft³ is the form used in metric documentation. Nothing changes between them, which means a figure quoted in one can always be checked in the other.
Our ten-carton example is 0.3 m³, which is 10.5944 CFT. The conversion block above the article does this in both directions if all you need is a unit change on a figure you already have.
The timber trade is where CFT shows up on its own terms, because sawn timber is bought and sold by the cubic foot rather than by the cubic metre. The arithmetic is identical — length by width by height, in feet — but the unit the invoice is written in is the one to match.
The formula, and a consolidation worked through
In metres the formula hides nothing: CBM = length × width × height × quantity.
A single carton first. 40 × 30 × 25 cm becomes 0.40 × 0.30 × 0.25 = 0.03 m³, and ten of those are 0.3 m³ — 300 litres, or 10.5944 CFT. Staying in centimetres gives the same answer by a different route: 40 × 30 × 25 = 30,000 cm³, and 30,000 ÷ 1,000,000 = 0.03 m³ per carton.
Now the case this page is really for. Ten cartons at 40 × 30 × 25 cm come to 0.30 m³. Two crates at 120 × 80 × 100 cm are 0.96 m³ each, so 1.92 m³. The consignment is 0.30 + 1.92 = 2.22 m³ across 12 pieces, which is 78.3986 CFT.
Average the two sizes first and you get a notional carton of 80 × 55 × 62.5 cm; twelve of those come to 3.3 m³. That is more than a cubic metre of difference on a small consolidation, and it is the difference a consolidator would invoice.
Quantity is a plain multiplier, which gives you a free check: if a declared volume is not a clean multiple of the single-carton volume, the error is in the measuring or the counting, not in the sum.
Measuring cartons so the figure survives the terminal
Freight is charged on the space a package takes up on the carrier's equipment, so what counts is the outside of the finished, packed carton — not the product, and not the carton's internal capacity.
Measure after packing, not before. A full carton bulges, and strapping, corner protectors and shrink wrap each add a little. Take the widest point.
If the cartons travel on a pallet, the pallet is part of the shipment. Enter the loaded pallet as a line of its own rather than the cartons individually — its footprint and its height are what occupies the container.
Round up. The terminal will round up when it measures, and a figure that is optimistic by a centimetre buys nothing.
Irregular shapes are charged on the rectangular space they need, so measure the box that would contain them rather than the shape itself.
Volume, volumetric weight and what a carrier bills
Volumetric weight expresses volume in kilograms so it can be compared with real weight. The carrier takes the shipment in cubic centimetres and divides by a number it publishes: length (cm) × width (cm) × height (cm) × quantity ÷ divisor.
Chargeable weight is then the greater of the actual weight and the volumetric weight. Dense cargo bills on what it weighs; light, bulky cargo bills on the room it occupies. That "whichever is greater" rule is the part that is genuinely standard across the industry. The divisor is not.
Published figures: 6000 is IATA's general rule for air cargo, 5000 is DHL Express's standard for its express products, 3000 corresponds to the 1:3 ratio used on rail and 1000 to the 1:1 ratio on sea LCL. Road freight has no general rule at all — the ratios vary by country and by carrier, so it is a question for whoever is quoting you.
The effect is large. Our 0.3 m³ is 300,000 cm³: 50 kg on a 6000 divisor, 60 kg on 5000, and 300 kg on the sea LCL 1:1 ratio. If those cartons really weigh 12 kg each, an airline bills the 120 kg actual weight, while the same consignment moving LCL is assessed on 300 kg.
Two cautions worth carrying into a booking. Carriers change divisors and apply different ones to different services, and some set a minimum chargeable weight per piece. And this page applies your chosen divisor to the whole shipment — a carrier that assesses each piece separately and rounds each one up will land slightly higher.
LCL, FCL and when the volume stops setting the price
Sea freight divides at roughly one container. Below that you are buying space inside a shared box — LCL — and the rate comes per cubic metre or per freight ton, the freight ton being whichever is greater of one tonne and one cubic metre. Above it you book a whole container at a flat rate, and the question changes from what the volume costs to whether the cargo fits.
Published internal volumes are the starting point for that second question. Hapag-Lloyd's example specifications give 33.2 m³ for a 20ft, 67.7 m³ for a 40ft and 76.3 m³ for a 40ft high cube, and the carrier's own page notes those are examples because containers differ by manufacturer.
Treat them as a ceiling nobody reaches. That volume assumes the box is packed corner to corner with no gaps. Pallets leave dead space along the walls, cartons cannot always be stacked to the roof without crushing, the door aperture is narrower than the container, and the payload limit can stop you well before the volume does.
So the container line in the result is a share of a geometric volume, and it says so. Whether a consignment actually loads is what a forwarder's load plan tells you.
Where a declared CBM usually goes wrong
The wrong power of ten. Centimetres become cubic metres by dividing by 1,000,000 and millimetres by 1,000,000,000, because the conversion is cubed along with the dimensions. Dividing centimetres by 100 is out by a factor of ten thousand.
Product dimensions instead of carton dimensions. What ships is the packed box. Packaging, void fill and the carton walls all add volume that is charged for.
One averaged carton standing in for several sizes. Covered above, and worth repeating because it does not look like an error on the page.
Mixing up CBM and volumetric weight. One is a volume and one is a weight, joined by a divisor the carrier chooses. A consignment has one CBM and as many volumetric weights as there are divisors.
Reading a container's capacity as usable space. Internal volume measures an empty box; loading efficiency is a separate question, and for palletised cargo the practical figure is a good deal lower.
What this page does not know
It calculates volume and converts units. It holds no freight rates, no carrier tariff and no customs rule for any country, and it cannot tell you what a shipment will cost. The cost line multiplies your volume by a rate you supply, which leaves out minimum charges, surcharges, a freight-ton basis, local handling and everything else that appears on a real invoice.
Volumetric weight is worked out across the whole shipment on the divisor you pick. A carrier may use a different one, assess each piece separately, or apply a minimum, so treat the figure as a way of checking a quote rather than predicting one. Container capacities are geometric volumes from a published specification and say nothing about whether your cargo will load.
Each carton edge is capped at 100 m and each line at 1,000,000 pieces — far beyond any real consignment, and enough to keep the exact arithmetic instant. Everything runs in your browser and nothing you type leaves the page.
Sources and methodology
The unit conversions are exact by definition and are implemented as exact ratios rather than decimal approximations: 1 inch = 2.54 cm and 1 foot = 0.3048 m exactly (NIST, Guide to the SI, Appendix B), and the litre is exactly one cubic decimetre, so 1 m³ = 1,000 L.
The 6000 divisor and the rule that the greater of actual and volumetric weight is billed come from IATA's material on air cargo tariffs and rules. The 5000 divisor is DHL Express's published standard. The 1:3 rail and 1:1 sea ratios, and the note that road ratios vary, come from DHL Global Forwarding's guide to chargeable weight.
Container capacities of 33.2 / 67.7 / 76.3 m³ are Hapag-Lloyd's published example specifications, quoted together with that carrier's own caveat that specifications vary by manufacturer.
Every worked figure on this page is recalculated by tests/cbm-lib.test.js and checked there against a hand calculation, so the prose and the calculator cannot drift apart.