345 cartons fit a 20ft container, and you will not load 345
A 60 × 40 × 40 cm carton is 0.096 m³. A 20ft dry container is about 33.2 m³ inside. Divide one by the other and 345 cartons fit.
No they don't. But the number is still worth having, as long as you know what kind of number it is.
| Container | Internal volume | Cartons by volume | 400 cartons fill | Containers needed |
|---|---|---|---|---|
| 20ft | 33.2 m³ | 345 | 115.66% | 2 |
| 40ft | 67.7 m³ | 705 | 56.72% | 1 |
| 40ft high-cube | 76.4 m³ | 795 | 50.26% | 1 |
Everything the division ignores
Cartons do not tessellate into a steel box. The division assumes your cargo is a liquid that takes the container's shape, and it isn't:
- Stacking geometry. 60 cm does not divide neatly into a container's internal length or width, and the remainder is dead air at one end.
- Pallets. If the goods are palletised, you are loading pallets, not cartons, and the pallet's own footprint and deck height come out of the cube before your cargo does.
- Weight. A container has a payload limit as well as a volume. Dense cargo hits the weight ceiling with the box half empty, and no amount of volume arithmetic will tell you that.
- Bracing and access. Dunnage, airbags and a door-end gap you can actually work in are all real and all volume — and the door opening is smaller than the box behind it, so the last row has to fit through it.
- Stacking limits and orientation. Cartons that cannot bear weight cannot go to the roof, and anything marked this-way-up loses the rotations that make a tight fit possible.
A commonly used planning haircut is 80–85% of the geometric figure, which would put this load nearer 293 cartons a container than 345. That is a rule of thumb, not a measurement — your packer's actual stack plan beats it every time.
Where the ceiling earns its keep
The honest use of the number is as an upper bound for a decision you make before anyone stacks anything. Here, 400 cartons is 115.66% of a 20ft — so two 20ft containers, each running comparatively empty — against 56.72% of a single 40ft. That comparison survives the haircut, because the haircut applies to both sides. A ceiling is a bad loading plan and a perfectly good way to choose an equipment type.
Weight will stop you first, often
A 20ft container has a payload limit in the region of 28 tonnes, and road limits in many countries bite well before that. Spread over its 33.2 m³, 28 tonnes is about 0.84 tonnes per cubic metre: cargo denser than that reaches the weight limit before the box is full, and at about 1.69 tonnes per cubic metre the container leaves half its space empty.
So the honest capacity is the lower of two numbers: how many cartons fit, and how many the axle limits allow. The calculator answers the first; only you know the second, and for dense goods it is the one that decides.
Choosing between the three sizes
On these cartons a 40ft holds 705 against a 20ft's 345, and a 40ft high-cube 795. The high-cube's extra foot of height is nearly free on stackable cargo and worth nothing on cargo that cannot be stacked any higher.
The comparison worth making is cost per carton shipped rather than cost per container. A 40ft rarely costs twice a 20ft, so for anyone with the volume the larger box is usually cheaper per unit — and for anyone without it, a part-filled 40ft is the most expensive way to move cargo there is.
How to use the ceiling properly
It answers one question well: is this shipment obviously too big, obviously too small, or near the line? For the first two the arithmetic is enough. For the third, ask the forwarder for a loading plan — they will do it for nothing, and within about 15% of a container boundary is exactly where the ceiling and the real load disagree.
Then keep score. Record what actually loaded against what the calculator predicted for a few shipments; the ratio is stable for a given cargo and packing method, and once you know your own you can use it instead of a generic 85%.
Work it for your own shipment
The figures above come from the same code the calculators run, so typing these inputs in reproduces them exactly. Your own numbers are the point though — size your own cartons against each container in the container load calculator, and check the chargeable weight if you are shipping air rather than sea.
These are estimates, not assessments. Duty rates, the taxable base, and the valuation rules that decide them are set by national law and by how your goods are classified. A customs broker or your national customs authority gives you the binding answer; this site gives you the arithmetic so you know roughly what is coming and which question to ask.