Most container problems surface at the terminal, not at the booking.

The machine measures 2.35 m on the drawing. The container’s internal height is 2.39 m. It still will not go in, because the door opening is 2.28 m. That gap is behind a good share of the re-bookings we handle.

Two other figures cause the same kind of trouble: the floor rating, and what the truck can legally weigh on the road at the destination.

Below are the container types you will be quoted, what they measure, and what each one is for. Treat the figures as typical — they vary slightly between manufacturers and operators, so if your cargo sits within a few centimetres of a limit, check the actual container’s specification before you book.

The containers most cargo moves in

Internal L Internal W Internal H Door opening (W × H) Volume Typical max payload
20 ft GP 5.90 m 2.35 m 2.39 m 2.34 × 2.28 m ~33 m³ ~28,200 kg
40 ft GP 12.03 m 2.35 m 2.39 m 2.34 × 2.28 m ~67 m³ ~26,700 kg
40 ft High Cube 12.03 m 2.35 m 2.70 m 2.34 × 2.59 m ~76 m³ ~26,500 kg
45 ft High Cube 13.56 m 2.35 m 2.70 m 2.34 × 2.59 m ~86 m³ ~27,600 kg

These take palletised freight, boxed goods, bagged material, appliances, furniture, and machinery that fits through the doors — anything that does not require temperature control, top loading or extra width.

The high cube is worth knowing about for one reason: the extra 30 cm of internal height. Plenty of cargo is quoted on a 40 GP and comes back needing a 40 HC once the stack height is checked. Better to settle that before the booking than after.

The door opening is smaller than the container

Worth stating plainly, because this is where most problems start.

A 40 GP gives you about 2.39 m of internal height and about 2.28 m at the door. Anything taller than the door will not load, however much space remains above it once inside. Width works the same way.

So when cargo is close to a limit, the door opening is the figure to check. It is also the point at which a standard container stops being an option and the special types below come into play.

Payload rating is not what you can load

The payload column above is what the container is rated to carry. It is not what you can legally put on a US road.

Road limits apply to the whole combination: tractor, chassis, the container’s own tare, and your cargo. A 40 ft rated for roughly 26,700 kg of payload will not be loaded to that figure if the combination then exceeds the gross vehicle weight limit. On the Interstate System that federal limit is 80,000 lb (about 36,300 kg) unless a permit is in place, and individual states apply their own limits on top.

Two consequences follow, and both surprise importers:

A 20 ft carries more weight than a 40 ft. About 28,200 kg against 26,700 kg. On dense cargo — machinery, tiles, stone, bagged resin — the 20 ft is sometimes the only container that can legally take the load, even though it costs more per cubic metre.

Heavy cargo reaches its weight limit before it fills the container. If you hit the payload while space remains, you are paying for volume you cannot use. The usual answers are to book on weight and accept the empty space, or to split the shipment across two containers.

The special container types

These are booked when a standard container cannot do the job.

Type Typical internal (L × W × H) What it is for
Open top 5.89 × 2.34 × 2.34 m (20 ft)<br>12.02 × 2.34 × 2.34 m (40 ft) Cargo taller than a door opening, craned in from above
Flat rack 5.64 × 2.44 m platform (20 ft)<br>12.12 × 2.44 m platform (40 ft) Overwidth, overheight, or heavier than a container floor will accept
Reefer 5.44 × 2.29 × 2.26 m (20 ft)<br>11.59 × 2.29 × 2.56 m (40 ft HC) Cargo requiring a controlled temperature for the whole voyage
ISO tank ~24,000–26,000 litres Liquids in bulk — chemicals and food-grade product
Platform / bolster Varies Heavy cargo shipped as a flat package, without a container

A few points that matter in practice:

Open top and flat rack both require a crane at each end. Neither is loaded by forklift from a ramp. If the factory cannot lift the cargo, or the consignee cannot, the container type is not available to you — however well it fits on paper.

Flat rack cargo is frequently stowed on deck, which means weather exposure. That changes the packing requirement, and the carrier can still refuse the stow on dimensions. How to choose between the two is covered in open top or flat rack for oversized machinery.

A reefer is smaller inside than it looks from outside. Insulation and the refrigeration unit take up wall thickness, so a 40 ft reefer HC holds less than a 40 ft GP of the same external length.

ISO tanks are not a general-purpose option. They are booked for liquids, and the tank grade matters if the previous contents are relevant to yours.

Volume or weight — which limit comes first?

Cargo The limit you reach first What to book
Light and bulky — furniture, panels, packaging, foam Volume 40 ft HC — the extra height is free capacity
Dense — machinery, tiles, stone, metal, liquids Weight 20 ft, after checking the payload against the road limit
Taller than 2.28 m Door height Open top
Wider than 2.34 m, or beyond the floor rating Door width or floor load Flat rack
Requires a set temperature Temperature Reefer
Is a liquid Containment ISO tank

Heavy equipment is where this stops being a category question and becomes a per-machine one. A machine with a long bed and moderate weight may suit an open top, while a denser machine with a small footprint is stopped by floor loading before size comes into it — the pattern with plastic machinery, and the reason laser cutting machines are usually decided on bed dimensions rather than weight.

Three figures decide the container: the door opening (not the internal dimension), the floor rating and payload, and the road weight limit at the destination. Everything else is cost.

If your cargo is close to any of them, treat it as over the limit until someone confirms otherwise. When it is time to book, the ocean freight service covers routing and equipment.