CBM is simply cubic metres, and it is the unit that decides what a large part of international freight costs. Ocean groupage, road groupage and warehouse storage are all priced by the cubic metre, so the difference between a quotation you can trust and one that surprises you at invoicing usually comes down to whether the CBM figure was calculated correctly. This CBM calculator converts carton dimensions and a quantity into total volume, and then does the part most tools skip: comparing that volume with the shipment's actual weight to show which of the two you will be billed on.
Arb Digital builds free tools that answer the question behind the question. A shipper asking for CBM almost always really wants to know what the freight will cost and whether the load fits a container. The calculator above therefore reports volume per carton, total volume in both metric and imperial units, the chargeable weight under four common pricing bases, and the percentage of a chosen container the shipment occupies — with a bar showing how the volume and weight compare.
What This CBM Calculator Does
Enter the outside dimensions of one carton, pick the unit those dimensions are in, and enter how many cartons there are and what each one weighs. The tool multiplies length by width by height to get the volume of a single carton in cubic metres, multiplies by the quantity for the shipment total, and converts to cubic feet using the exact factor of 35.314 666 72 cubic feet per cubic metre.
It then computes chargeable weight on whichever basis you select. Sea LCL conventionally treats one cubic metre as equivalent to one tonne and bills on whichever is greater, a convention usually written W/M for weight or measurement. Air freight uses a dimensional divisor of 6,000 when dimensions are in centimetres, which works out to 167 kilograms per cubic metre. Express courier services commonly use 5,000, giving 200 kilograms per cubic metre, and road groupage often works to about 333 kilograms per cubic metre. Selecting the wrong basis is the most common reason a self-calculated freight estimate misses.
Finally it compares total volume against the nominal internal capacity of a container you choose, showing the fill percentage and how many containers the load would need. That figure is a planning aid rather than a loading plan, and the section below explains exactly why the practical limit is lower than the arithmetic suggests.
How to Use It
- Measure the packed carton, not the product. Include the packaging, any protruding corner protectors and the natural bulge of a filled box. Carriers measure the widest point.
- Enter the quantity of cartons. If your shipment has several different carton sizes, run the tool once per size and add the totals — mixing sizes into one average produces a misleading answer.
- Enter the gross weight per carton. Gross means the product plus its packaging, since that is what the carrier weighs.
- Select the pricing basis that matches your mode. Sea, air, courier and road all convert volume to weight differently, and the difference between them is large.
- Check the fill percentage before booking. If a load comes out near or above the nominal container capacity, treat the arithmetic as optimistic and speak to your forwarder about a loading plan.
The Formula: How CBM Is Calculated
The volume of a single carton is CBM = L × W × H with every dimension expressed in metres. Total shipment volume is that figure multiplied by the number of cartons. The metre and the cubic metre are defined in the BIPM SI Brochure, and NIST's guidance on SI units covers the derived units and prefixes used in trade documentation.
Work the default example. A carton measuring 40 × 30 × 25 cm converts to 0.40 × 0.30 × 0.25 m, which is 0.03 m³ per carton. Multiply by 100 cartons and the shipment is 3.0 m³, or 105.94 cubic feet. Gross weight is 100 × 12 = 1,200 kg. On a sea LCL basis, 3.0 m³ is treated as equivalent to 3,000 kg, which exceeds the actual 1,200 kg, so this shipment is billed on volume at three revenue tonnes. On an air freight basis at 167 kg per cubic metre, the volumetric weight is only 501 kg, so air freight would bill the actual 1,200 kg instead.
That reversal is the whole point of the comparison. The same physical shipment is a volume shipment by sea and a weight shipment by air, purely because the two modes value space differently. There is no universal answer to "is my cargo heavy or light" — it depends entirely on the divisor being applied.
The conversion to cubic feet is exact rather than approximate: one foot is exactly 0.3048 metres by definition, so one cubic metre is exactly 35.314 666 72 cubic feet. Rounding that to 35.3 introduces an error of about one part in three thousand, which is immaterial for a single carton and visible on a full container.
Why a Container Never Holds Its Nominal Capacity
The internal capacities in the selector — around 33 m³ for a 20-foot general purpose container, 68 m³ for a 40-foot and 76 m³ for a 40-foot high cube — are geometric volumes, calculated from internal length, width and height. Container classification and external dimensions are set by ISO 668, the international standard for series 1 freight containers, and internal capacity varies slightly between manufacturers within those limits.
Real loads reach 80 to 90 percent of that figure at best, for reasons that are pure geometry rather than inefficiency. Cartons rarely tessellate perfectly into a container's footprint, so there is dead space at the end of every row. Pallets add their own height — a standard pallet is around 15 cm before any goods are stacked on it — and that height is lost across the entire floor area. Nothing can be stacked to the exact roof line because the load must be secured and the doors must close. And many cargoes cannot be stacked at all beyond a certain height, either because of crush strength or because of the way they are packed.
Weight limits bite before volume for dense cargo. A 20-foot container has a payload limit in the region of 28 tonnes, which is reached at well under half its volume for anything like tiles, liquids or machinery. If your fill percentage looks comfortable but the total weight is high, weight is the binding constraint and the volume figure is irrelevant.
Chargeable Weight Explained Properly
Carriers sell space and lift capacity at the same time, and a purely weight-based tariff would lose money on light bulky freight while a purely volume-based one would lose money on dense freight. Chargeable weight resolves that by billing on whichever of actual weight and volumetric weight is greater.
Volumetric weight is obtained by dividing the volume by a divisor set by the carrier. With dimensions in centimetres, the classic air freight divisor of 6,000 means a box of 6,000 cm³ is charged as one kilogram — equivalent to 167 kg per cubic metre. Express operators generally use 5,000, which is 200 kg per cubic metre and therefore more expensive for bulky goods. Sea LCL uses the far more generous ratio of 1,000 kg per cubic metre, which is why bulky low-value goods travel by sea.
Knowing which side you are on tells you which change actually saves money. If you are billed on volume, reducing packaging size cuts the bill and removing weight does nothing. If you are billed on weight, the reverse is true and shrinking the box is wasted effort. The bar chart above shows the ratio directly, and the dimensional weight calculator works the same relationship from the parcel side.
Measuring Cartons So the Carrier Agrees With You
Freight disputes over volume are common and almost always come down to measurement practice. Carriers measure the maximum external dimensions of the item as presented, which means a filled carton is measured at its bulge, not at the flat dimension printed on the box. A carton nominally 40 cm wide that bulges to 42 cm is measured as 42.
Palletised freight is measured as the whole pallet — its full footprint and its full height including the pallet itself, plus any overhang. A 120 × 100 cm pallet loaded to 150 cm total height occupies 1.8 m³ regardless of how efficiently the cartons are arranged on it. If you are shipping on pallets, enter the pallet dimensions here rather than the carton dimensions, with a quantity of pallets.
Round dimensions up to the nearest centimetre, since most tariffs do the same. And measure after packing rather than before: shrink wrap, edge protectors and strapping all add a little, and the total can move a shipment across a rate break. For general unit handling the volume converter and the unit converter cover conversions this page does not, and the square footage calculator handles warehouse floor area.
Using CBM in Costing and Quoting
Once you have a reliable CBM figure, per-unit landed cost becomes straightforward. Divide the freight charge by the number of saleable units in the shipment to get freight per unit, then add it to the product cost before setting a price. The shipping cost per item calculator does exactly that allocation, and the wholesale price calculator takes the result through to a selling price.
CBM also drives warehouse costs, which are typically quoted per cubic metre per week or per pallet position per month. A shipment that looks cheap to move can be expensive to hold if it is bulky, so it is worth running the volume figure through both calculations before committing to an order quantity.
One planning habit is worth adopting: calculate CBM before finalising packaging design, not after. Reducing a carton from 40 × 30 × 25 to 38 × 28 × 23 cm cuts volume by nearly 19 percent, and on a volume-billed shipment that is a straight 19 percent off the freight line. Packaging decisions made at the design stage are almost always cheaper than freight negotiations made later. The complete set of tools is on the free online tools hub.
Arb Digital builds free tools like this one because useful pages earn attention. If you want tools, calculators or content built for your own audience, we can help.
Browse All Free Tools Talk to Arb DigitalCommon Mistakes to Avoid
- Measuring the product instead of the packed carton — packaging, protectors and bulge all count, because the carrier measures what arrives at the dock.
- Mixing centimetres and metres — a single misplaced decimal changes the volume by a factor of a million. Set the unit selector and enter raw numbers.
- Assuming a container holds its nominal volume — 80 to 90 percent is a realistic ceiling once pallets, stacking limits and door clearance are accounted for.
- Using the air divisor for a sea shipment — sea LCL treats a cubic metre as a tonne, air treats it as about 167 kilograms. Using the wrong one misstates the cost badly.
- Averaging mixed carton sizes — calculate each size separately and add the volumes, because an average carton does not exist in the container.
Related Free Tools From Arb Digital
For the parcel-side version of chargeable weight, use the dimensional weight calculator. For allocating freight to units, the shipping cost per item calculator, and for pricing the result, the wholesale price calculator. Unit conversions belong in the volume converter or the unit converter, warehouse area in the square footage calculator, and bulk material volumes in the cubic yard calculator. The free tools hub lists the rest.
Frequently Asked Questions
Cubic metre. It is the standard volume unit in international freight, used to price ocean groupage, road groupage and warehouse storage. One cubic metre equals exactly 35.314 666 72 cubic feet.
The packed carton, at its widest point. Carriers measure the item as it is presented, including packaging, corner protectors and any bulge in a filled box, so a measurement taken from a drawing will usually understate the billed volume.
The carrier compares actual gross weight with volumetric weight and bills whichever is greater. Volumetric weight comes from dividing volume by a divisor: about 167 kilograms per cubic metre for air freight, 200 for express courier and 1,000 for sea LCL.
Because cartons do not tessellate perfectly, pallets add height across the whole floor, the load must be secured and the doors must close, and many cargoes cannot be stacked to the roof. Eighty to ninety percent of nominal volume is a realistic ceiling.
Calculate each size separately and add the volumes together. Averaging the dimensions produces a figure that does not correspond to any real carton and will not match what the carrier measures.
If the goods travel palletised, enter the pallet footprint and the full loaded height including the pallet, with the number of pallets as the quantity. Palletised freight is measured as a whole unit rather than carton by carton.
Whichever limit you reach first. Dense cargo such as tiles or liquids hits the payload limit at well under half the volume, while light bulky goods fill the space long before the weight limit. Check both before booking.
This tool is provided for planning and estimation only. Container capacities are nominal and vary by manufacturer, and chargeable weight rules differ between carriers — confirm the applicable rates and dimensions with your freight forwarder before booking.
