Short answer
In sea freight, the main types are the 20' and 40' standard, the 40' High Cube, reefer, open top, flat rack, and tank containers. The internal volume of a 20' standard is approximately 33 m³, a 40' standard approximately 67 m³, and a 40' High Cube approximately 76 m³. The threshold depends on the container type: about 0.85 tons/m³ for a 20' DV, 0.40 for a 40' DV and 0.35 for a 40' HC; above these values the limiting factor is weight, not volume.
What is a container, and why do types differ
A container is a cargo box whose external dimensions and corner fittings are standardized under ISO, allowing cargo to be transferred between ship, truck, and train without being handled. It is the external dimensions that are standard. Internal dimensions vary by a few centimeters depending on wall thickness, manufacturing year, and carrier. The values in this guide are therefore typical values; for the exact figure to write into a contract or loading plan, the figure should be measured on the allocated container or confirmed from the carrier’s own technical spec sheet for that type; the markings on the door (tare, net load, cubic capacity) do not give internal dimensions. The CSC plate does not give internal dimensions; it carries approval information, date of manufacture, maximum gross weight, stacking weight, and strength test values.
Width barely ever changes. Variation occurs in three places: height (High Cube), wall structure (reefer insulation), and body shape (open top, flat rack, tank).
20’ and 40’ standard container dimensions
The type known in the market as dry van or DV is the closed container that carries the large majority of general dry cargo.
| Type | Internal length | Internal width | Internal height | Internal volume | Tare | Max. gross |
|---|---|---|---|---|---|---|
| 20’ DV | ~5.90 m | ~2.35 m | ~2.39 m | ~33 m³ | ~2.2 t | 30,480 kg |
| 40’ DV | ~12.03 m | ~2.35 m | ~2.39 m | ~67 m³ | ~3.7 t | 30,480 kg |
| 40’ HC | ~12.03 m | ~2.35 m | ~2.69 m | ~76 m³ | ~3.9 t | 30,480 kg |
Payload is found by subtracting the tare from the maximum gross weight: approximately 28 tons for a 20’ DV, and approximately 26.7 tons for a 40’ DV. In other words, the 40-footer gives twice the volume while carrying less weight than the 20-footer.
The 30,480 kg in the table is the ISO 668 type value; 40’ and 40’ HC units built for a maximum gross weight of 32,500 kg are common on the market, and some older 20-footers show 24,000 kg. The binding figure is always the maximum operating gross weight on that container’s own CSC plate.
A detail often overlooked is door opening. Door height is lower than internal height — approximately 2.28 m for a standard container and approximately 2.58 m for a High Cube. A long piece of machinery planned against the internal height may not fit through the door.
What High Cube gains, and what it doesn’t
The High Cube (HC) is only 1 foot (about 30 cm) taller than the standard container. Length and width are the same. The gain is purely in volume: 76 m³ instead of 67 m³, roughly 13% more.
This extra height helps in two situations. First, when a product box’s height falls just short of allowing an extra stacking layer in a standard container but fits in an HC. Second, for single-piece cargo whose height slightly exceeds 2.39 m.
What it does not gain is weight. Maximum gross weight is unchanged, its tare is slightly higher, so payload drops by a few hundred kilograms. In some countries, a truck loaded with an HC container may also push the total height close to road limits; a special trailer may be needed for inland transport.
Special-purpose containers
| Type | Internal length | Internal width | Internal height | Capacity |
|---|---|---|---|---|
| 20’ reefer | ~5.44 m | ~2.29 m | ~2.27 m | ~28 m³ |
| 40’ HC reefer | ~11.56 m | ~2.29 m | ~2.50 m | ~67 m³ |
| 20’ open top | ~5.90 m | ~2.35 m | ~2.35 m | ~32 m³ |
| 40’ flat rack | ~12.06 m platform; between end walls typically ~11.6–11.8 m | ~2.40 m | open | varies by type |
| 20’ tank | 20’ ISO frame | — | — | ~21,000–26,000 litres |
Reefer containers are for temperature-controlled cargo. Their internal volume is noticeably smaller than a dry container of the same length: insulation in the walls, floor, and ceiling takes up space on every side, the refrigeration unit at the front takes up length, and the T-shaped grating floor further reduces usable height. A reefer is not a freezer but a container that maintains temperature; cargo must be brought to the target temperature by pre-cooling before loading. Stacking must not exceed the red loading line on the ceiling, to allow air circulation.
Open top containers have a tarpaulin roof and removable roof bows. They are for cargo loaded from above by crane, whose height exceeds the container’s own height. Cargo that goes above the roof line is considered out of gauge and incurs additional charges.
Flat rack is a platform with no side walls or roof, with folding ends on most types. It is used for heavy machinery, boilers, generators, and similar cargo. Its point-load capacity is high but varies by type, so it should be confirmed with the carrier.
Tank containers are cylindrical tanks fitted into an ISO frame, used to carry liquid chemicals, liquid food products, and certain dangerous goods. Because of liquid surge, tanks are generally not filled to between 20% and 80% of their capacity; for dangerous goods, the maximum filling degree is set by the IMDG/ADR substance-specific formula (in most cases it does not exceed 95%).
How many pallets fit in a 20’ and 40’ container
Typical figures for a single-layer arrangement are as follows.
| Container | Euro pallet (120×80 cm) | Industrial pallet (120×100 cm) |
|---|---|---|
| 20’ DV | 11 | 9–10 |
| 40’ DV / 40’ HC | 23–24 | 20–21 |
The 11 for the 20’ is the theoretical upper limit; for the 40’ the theoretical upper limit is 25, and the 23–24 in the table is what typically fits in practice. Three things reduce these numbers in practice: cargo overhanging the pallet (stretch film and hanging cardboard add a few centimeters), pallets not being arrangeable in different orientations, and the cargo not being stackable in a second layer. Because internal width is only about 2.35 m, two Euro pallets cannot sit side by side with their 120 cm edges across (2.40 m); one pallet with its 120 cm edge across and a second with its 80 cm edge across (2.00 m in total) do fit. Reaching 11 pallets in a 20’ takes two columns laid out in different directions: 7 pallets across the width in one (80 cm deep each, 5.60 m) and 4 pallets lengthways in the other (120 cm each, 4.80 m). If the cargo can be stacked, it is weight and height that become decisive, not pallet count.
What limits the load: volume or weight
A container closes out either because its volume is full or because it has hit its weight limit. Which comes first is determined by the cargo’s density.
A 20’ DV’s roughly 28-ton payload corresponds to 33 m³ of volume — a threshold of about 0.85 tons per cubic meter. For a 40’ DV, it’s 26.7 tons and 67 m³, or about 0.40 tons per cubic meter. For a 40’ HC, it’s about 26.6 tons and 76 m³, or about 0.35 tons per cubic meter.
The result: for cargo with a density above 0.85 tons/m³, a 20’ container hits its weight limit before its volume is full. For marble, ceramics, metal profiles, glass, liquid-filled drums, cement, and similar cargo, half the container may sit empty, yet no more can be loaded. In a 40-footer, the usable volume is payload divided by density: at 0.85 tons/m³, 26.7 tons occupies about 31 m³, less than half of the 67 m³, and the share falls further as density rises. That’s why, for heavy cargo, two 20-footers are often more sensible than one 40-footer; however, the second box means a second freight charge, THC, road haul and handling, so the decision depends on comparing weight against cost per container.
Conversely, for low-density cargo such as furniture, packaging material, textiles, and plastic products, the weight limit is never approached; here the 40’ HC gives the lowest cost per cubic meter.
Common mistakes and points to watch
- Treating internal dimensions as exact figures. The values in tables are typical. If cargo is being planned to fit with no margin to spare, the dimensions should be measured physically on the allocated container or confirmed from the carrier’s technical spec sheet for that type.
- Confusing door opening with internal dimensions. The door is both lower and narrower. For single-piece machinery loads, measurements should be taken from the door.
- Assuming a 40-footer is twice a 20-footer. True for volume, not for weight. A 40-footer carries less payload than a 20-footer.
- Expecting extra tonnage from a High Cube. HC only gains volume; weight capacity does not increase.
- Neglecting VGM. Under SOLAS, declaring the verified gross mass of a loaded container is the shipper’s responsibility. A container without a declaration will not be loaded onto the vessel, and the cargo is delayed.
- Not accounting for road weight limits. The weight a container can carry and the weight a truck can legally carry from the port to the factory can differ. The limits of both the origin and destination country should be checked separately.
- Loading a reefer with warm cargo. The unit maintains temperature; it does not rapidly lower it. Without pre-cooling, temperature deviation is unavoidable.
- Leaving weight distribution unbalanced. If cargo is concentrated at one end of the container, axle-load limits are exceeded and handling risk arises. Heavy items should be spread across the floor and the middle section.
- Pricing out-of-gauge cargo as if it were a standard container. For open top and flat rack loads, dimension overhang is calculated separately and changes cost significantly.
Choosing a container type becomes clear once it is assessed together with cargo density, dimensions, and temperature requirements; working in advance with the sea freight operations team on line- and route-specific constraints strengthens the loading plan.
This page is general information, not legal advice. Regulations change; confirm the current position before acting.