What this calculator does
CBM — cubic metres — is the unit almost every freight conversation starts with. Enter the outer dimensions of one carton, how many you have, and (optionally) the gross weight of one, and this tool returns the total cube in both cubic metres and cubic feet, the total weight, the average density, the volumetric weight at the four conventional divisors, and roughly how much of a 20’ or 40’ container that consignment fills.
It is deliberately the shortest form on the site. If you need to know which basis a carrier will actually bill you on, use the chargeable weight calculator; this one just gives you the cube, fast and correctly.
The formula
V_carton = L × W × H ÷ 1 000 000 (m³, with L, W, H in cm)
V_total = n × V_carton (m³)
V_cft = V_total ÷ 0.028316846592 (ft³)
M_total = n × w (kg)
ρ = M_total ÷ V_total (kg/m³)
L, W, H are the outer dimensions of one packed piece in centimetres, n the quantity, and w the gross weight of one piece.
The cubic-foot conversion is exact, not approximate. One international foot is 0.3048 m by definition, so one cubic foot is 0.3048³ = 0.028316846592 m³ exactly, and 1 m³ = 35.31466672 ft³. Nothing in this tool uses a rounded factor.
The volumetric weight outputs use the same relation as any dimensional-weight tariff — W_vol = V_cm³ ÷ d — evaluated at the four divisors you will meet in practice:
6000 cm³/kg air freight → 1 m³ = 166.67 kg
5000 cm³/kg courier / express → 1 m³ = 200 kg
3000 cm³/kg road groupage → 1 m³ = 333.33 kg
1000 cm³/kg sea LCL (W/M) → 1 m³ = 1000 kg = 1 revenue ton
CBM vs CFT
They measure the same thing; which one you quote depends on who you are talking to. Ocean and air rate sheets, packing lists and shipping marks are in cubic metres almost everywhere, including in the United States for international moves. Cubic feet survives in US domestic trucking and LTL density calculations, in some warehousing contracts priced per cubic foot of storage, and in air cargo ULD capacity tables. If someone quotes you “35 cube” for a small consignment, establish which unit they mean before you agree a price — the factor between them is 35, and getting it backwards is a thirty-five-fold error.
Why stated container capacities overstate what you load
A 20’ GP measures about 5.90 × 2.35 × 2.39 m inside, which multiplies to roughly 33 m³. A 40’ HC comes out around 76 m³. Those are the numbers on the container spec sheet, and you will never load them, because a container is not a bucket:
- Pallets do not tile the floor. A 20’ GP takes 11 standard 1200 × 800 mm Euro pallets in a single layer. That is
11 × 1.2 × 0.8 = 10.56 m²of pallet on a floor of about5.90 × 2.35 = 13.9 m²— 76% of the floor, and the remainder is clearance you cannot fill with palletised cargo. - Cartons do not stack to the ceiling. The last layer is almost never a whole layer, and the top of the load must clear the door lintel, which is 10–15 cm lower than the internal roof.
- Dunnage, airbags and door clearance take real volume — typically 3–5% on a mixed load.
- The load must be safe. Cargo secured to the CTU Code (the IMO/ILO/UNECE Code of Practice for Packing of Cargo Transport Units) needs bracing space, and heavy items need weight distributed rather than optimally packed.
So planners work to usable volume, not internal volume. The rules of thumb this tool uses are ~28 m³ for a 20’ GP and ~67 m³ for a 40’ HC — about 85–88% of nominal. Treat the percentages it reports as a sanity check on whether you are in the right container, not as a loading plan.
Typical loadability factors
| Cargo form | Typical fill of nominal internal volume |
|---|---|
| Loose-loaded uniform cartons, hand-stowed | 85–95% |
| Palletised cartons, standard pallets | 70–85% |
| Mixed carton sizes on pallets | 60–75% |
| Irregular or crated machinery | 50–70% |
| Big-bag or drummed goods | 60–75% |
The other constraint is payload. A 20’ GP is commonly rated around 28 tonnes of cargo, a 40’ HC around 26 tonnes — but the binding limit is usually not the container at all, it is the road-legal gross combination weight and axle loading at the origin and destination, which differ by country and can cap you well below the box’s rating. Anything denser than about 1000 kg/m³ will weigh out before it cubes out in a 20’; below about 350 kg/m³ you will cube out first and should be looking at a 40’ HC even for a modest tonnage.
Worked example
250 export cartons, each 60 × 40 × 40 cm, each 12.5 kg gross.
Volume of one carton:
60 × 40 × 40 = 96 000 cm³ ÷ 1 000 000 = 0.096 m³
Total cube:
250 × 0.096 = 24.000 m³
In cubic feet, 24 ÷ 0.028316846592 = 847.55 ft³. Total gross weight is 250 × 12.5 = 3125 kg, so the average density is 3125 ÷ 24 = 130.2 kg/m³.
Against the usable-volume rules of thumb that is 24 ÷ 28 = 85.7% of a 20’ GP and 24 ÷ 67 = 35.8% of a 40’ HC. In other words: this is a full 20’ container’s worth of cargo with almost nothing to spare, and at 3.1 tonnes it is nowhere near any payload limit — a classic cube-out load.
The volumetric weight equivalents follow directly from the cube: 24 000 000 cm³ ÷ 6000 = 4000 kg on the air basis, 4800 kg at the express divisor of 5000, and 8000 kg at a road divisor of 3000. On sea LCL the weight-or-measure basis is 24 revenue tons, since 24 m³ beats 3.125 tonnes comfortably.
FAQ
Should I use the carton dimensions or the palletised dimensions? Whichever the carrier will measure. For LCL and air, that is the palletised or crated pack including overhang and wrap. For an FCL container plan, use the carton dimensions and let a load planner deal with the stacking — the palletised cube would double-count the air between cartons.
Why does the tool say 28 m³ for a 20’ when the spec sheet says 33? Because 33 m³ is the internal geometry and 28 m³ is what fits. The difference is stacking and securing loss, not a measurement error. If you are loose-loading uniform cartons by hand you will beat 28; if you are on pallets you may not reach it.
Do I round the dimensions before calculating? Not for planning a container — use the real dimensions. For a chargeable weight on air or express, yes: most carriers round each dimension up to the next whole centimetre before cubing. The chargeable weight calculator has that switch built in.
What is a revenue ton? The sea LCL billing unit: the greater of one cubic metre and one tonne, per unit of cargo. Quoted as “per W/M” (weight or measure) or “per R/T”. A 24 m³ / 3.1 t consignment is 24 revenue tons; a 3 m³ / 8 t consignment is 8.
Is CBM the same as a loading metre? No. A loading metre (LDM) is one metre of trailer length across its full 2.40 m width — a floor-area measure used in European road groupage, not a volume. One LDM is conventionally rated at around 1750 kg. If you are quoting road freight in Europe, the LDM figure will often govern rather than the cube.
This tool provides indicative figures for planning and quoting. Usable-volume and payload figures are rules of thumb; confirm the internal dimensions, tare and rated payload of the specific container, and the road weight limits applicable at each end, before committing to a booking.