The standard dry container
The dry container, also called a general-purpose or GP container, is the default unit in ocean freight. It has a rigid steel roof, solid side walls, and two swing doors at one end. It is designed for anything that does not need temperature control and can be loaded through a standard door opening.
Two lengths dominate:
- 20ft dry (1 TEU): External dimensions roughly 6.1 m long x 2.44 m wide x 2.59 m high. Internal volume around 33.2 cbm. Maximum payload approximately 21,727 kg. Used for dense, heavy cargo where weight fills the box before volume does.
- 40ft dry (2 TEU): External dimensions roughly 12.2 m long x 2.44 m wide x 2.59 m high. Internal volume around 67.5 cbm. Maximum payload approximately 26,680 kg. Used for lighter, bulkier cargo where volume fills the box before weight does.
- 40ft High Cube (40HC): Same footprint as the 40ft but 2.9 m high externally, giving around 76.4 cbm internally. The most common unit for e-commerce, furniture, and anything that benefits from the extra 30 cm of headroom.
Weight versus volume
A 20ft container is heavier relative to its volume than a 40ft. If your cargo is dense, such as machinery or minerals, the 20ft often makes sense because you hit the weight limit before you run out of floor space. If your cargo is light but bulky, such as furniture or plastic goods, the 40ft or 40HC gives you more room per dollar of freight rate. Always check both the volume and the weight limit before booking.
High Cube containers
A High Cube is simply a standard dry container built 30 cm taller than the ISO standard height. The 40ft High Cube is now more common than the standard 40ft on most trades, and the 20ft High Cube exists but is less widespread. The extra height matters for cargo that stacks tall, for machinery with a large footprint, and for loading with a forklift inside the container. Freight rates for 40HC units are often the same as or only marginally above a standard 40ft, making it the default choice when the cargo fits.
Reefer containers
A reefer container is a refrigerated container with an integrated refrigeration unit at one end. It maintains a set temperature throughout the voyage, from around -30 degrees Celsius for frozen cargo up to +30 degrees for cargo that needs to be kept warm. The internal dimensions are slightly smaller than a dry container of the same external size, because the insulated walls take up space.
- 20ft reefer: Internal volume around 28 cbm. Payload roughly 21,600 kg. Used for smaller volumes of frozen or chilled cargo.
- 40ft reefer: Internal volume around 59 cbm. Payload roughly 27,700 kg. Used for larger volumes and for cargo that needs consistent temperature over long voyages.
- 40ft High Cube reefer: The most common reefer unit today, with around 67 cbm internal volume.
Reefer containers require a power socket at every point in the journey: at the origin terminal, on the vessel (a ship has a limited number of reefer plugs), at transhipment ports, and at the destination terminal. Booking a reefer means confirming reefer plug availability along the entire route, not just at the two ends.
Reefer versus climate-controlled
A reefer actively refrigerates and can hold a precise set temperature throughout the voyage. A controlled-atmosphere or modified-atmosphere container goes further for perishables like fresh produce, adjusting the mix of gases as well. A simple insulated container without a compressor is not a reefer and will not hold temperature on a long voyage. If your cargo has a temperature requirement, you need an active reefer, not just insulation.
Open top containers
An open top container is a dry container with the roof replaced by a removable tarpaulin or bows. Cargo is loaded from above by crane rather than through the end doors. This matters for cargo that is too tall to fit through a standard door opening, such as large machinery, coils of steel, or stone slabs.
Open tops carry an over-height surcharge when cargo protrudes above the container frame, called over-height or out-of-gauge cargo. The carrier needs to know the exact stowage height because the container may not be able to be stacked normally on the vessel. Dimensions match the equivalent dry container length, but internal height is slightly less because the door header takes up space at the end.
Flat rack containers
A flat rack has a floor and two end walls, but no roof or side walls. Some have fixed end walls, others have collapsible end walls that fold down flat for empty storage. Flat racks are used for oversized cargo that is too wide, too tall, or too heavy to fit in or be loaded into a closed container: construction equipment, boats, large industrial components, and project cargo.
- 20ft flat rack: Floor length around 5.64 m, width around 2.23 m. Maximum payload around 45,000 kg.
- 40ft flat rack: Floor length around 12.13 m, width around 2.23 m. Maximum payload up to 40,000 kg depending on the unit.
Cargo on a flat rack is secured with lashing rings and chains. Because there are no side walls, the cargo is exposed on board, and rain covers or shrink wrap may be needed for weather protection. Flat rack bookings require an out-of-gauge declaration and the carrier may need to place the unit in a specific position on the vessel, which affects availability and cost.
Tank containers
A tank container is a cylindrical tank mounted inside an ISO frame. It is used for bulk liquids, gases under pressure, and hazardous materials that cannot be shipped in drums or flexibags. Common uses include chemicals, food-grade liquids such as edible oils and fruit juice concentrates, and industrial gases.
Tank containers are governed by the IMDG code for hazardous cargo and by specific ISO tank standards (T-codes) that define the pressure rating, material, and fittings appropriate for each liquid type. A T11 tank, for example, is used for many non-hazardous liquids, while a T14 is required for more aggressive chemicals. The tank owner or the forwarder must confirm the right T-code for your specific cargo before booking.
Platform and special units
A platform container is flat rack with no end walls at all: just the floor on the ISO frame. It is used for very large, heavy cargo where any end wall would obstruct loading or overhang. Beyond these standard types, carriers operate specialist units for specific trades: ventilated containers for cargo that needs airflow such as coffee and cocoa, insulated containers without active refrigeration, and bulk containers with a top hatch for loading granular cargo.
Choosing the right container
The right container depends on four things: whether the cargo needs temperature control, whether it fits through a standard door, whether it fits within the external dimensions of a closed container, and whether its weight is within the payload limit. For most cargo, a 40ft High Cube dry container is the answer. For temperature-sensitive cargo, a reefer of the matching size. For anything oversized or top-loaded, an open top or flat rack. For bulk liquids, a tank.
Always verify internal dimensions, not external. The usable floor length of a 20ft container is around 5.9 m, not 6.1 m. The usable internal width is around 2.35 m. A pallet that is 1.2 m x 1.0 m fits two-abreast with room to spare; a 1.2 m x 1.2 m Euro pallet fits in a single row only. These numbers matter before you book, not after the cargo arrives at the terminal.
The bottom line
Container types are not interchangeable. A dry box cannot keep cargo cold, an open top costs more and needs pre-approval, and a flat rack requires lashing and an out-of-gauge declaration. Choosing the right type from the start is straightforward when you know what each is built for. Match the container to the cargo's temperature requirement, its loading method, its dimensions, and its weight. Get those four things right and the rest of the shipment follows from there.