An ISO container is a standardised intermodal freight container built to specifications set by the International Organization for Standardization. Standardisation is what lets the same box move between ship, rail, and road without the goods inside being touched at any transfer point.
What Does the ISO Standard Actually Govern?
External dimensions, corner castings, floor strength, and stacking load. Those four elements have to match across every container in world circulation, and fixing them is what makes a box loaded in Shanghai fit a chassis in Antwerp without anyone measuring anything.
Three ISO standards do most of the work. ISO 668 sets base dimensions and weight ratings. ISO 6346 governs the identification code stencilled on every container, which is how a specific box gets tracked across carriers and terminals. ISO 1496 covers structural testing — what a container must survive before entering service.
The organisation writes standards rather than building containers. Manufacturers construct to specification and containers are certified against it, which is why boxes from different builders behave identically on a terminal. Container dimensions and weight ratings sit among the freight and road transport terms that determine how a load moves once it reaches the road leg.
What Sizes Do ISO Containers Come In?
Two lengths carry the bulk of world container traffic: 20ft and 40ft. Both share an external width of 2.44 m and standard height of 2.59 m.
A 20ft container measures 6.06 m long externally. A 40ft measures 12.19 m. Width and height stay constant across both, which is what allows them to stack together and share handling equipment.
The 40ft high cube adds height without changing the footprint, standing 2.90 m externally instead of 2.59 m. That extra height suits light, bulky cargo that runs out of volume before it runs out of weight.
The 45ft pallet-wide container exists largely for European traffic. Its internal width accommodates Euro pallets more efficiently than a standard box, and it appears on short-sea and rail routes across the continent rather than on deep-sea services.
How Much Can an ISO Container Carry?
Weight capacity does not scale with length, and this catches out shippers loading dense cargo. Both the 20ft and the 40ft carry a maximum gross weight of 30,480 kg under the ISO standard — the same ceiling for a box twice the length.
Tare weight is what differs. An empty 20ft weighs 2,200 kg; an empty 40ft weighs 3,750 kg. Subtract each from the same gross ceiling and the 20ft carries more cargo weight than the 40ft, despite holding half the volume.
Volume runs the opposite way. A 20ft offers 33 m³ of internal capacity, a 40ft 67 m³, and a 40ft high cube 76 m³.
That split decides which box to book. Dense cargo — tiles, machinery parts, tinned goods, liquids in drums — fills a 20ft to its weight limit with space to spare. Light, bulky cargo fills a 40ft to its roof long before weight becomes a constraint. Booking a 40ft for dense freight buys volume that cannot legally be used.
What Types of ISO Container Are Used in Freight?
Five types cover most commercial freight movement. Dry van containers are the standard enclosed box and carry general cargo. Reefer containers run integrated refrigeration for temperature-controlled goods. Open top containers replace the fixed roof with a removable cover so cargo loads by crane from above. Flat racks drop the sidewalls entirely, carrying machinery and oversized items that fit inside nothing. Tank containers hold a cylindrical vessel inside an ISO frame for liquids and gases.
All five share the same external dimensions and corner fittings, which is the point of the standard — a flat rack and a reefer stack and handle identically even though what they carry has nothing in common.
What Do TEU and FEU Mean?
TEU stands for Twenty-foot Equivalent Unit and measures container capacity rather than counting containers. One 20ft box is 1 TEU. One 40ft box is 2 TEU, expressed as 1 FEU — Forty-foot Equivalent Unit.
The measure exists because counting boxes tells you nothing useful when they come in two lengths. Vessel capacity, terminal throughput, and port rankings all run in TEU. The Port of Antwerp-Bruges is the second largest container port in Europe on that measure, putting Belgium at the front of European container traffic and generating a corresponding volume of inland road movements.
How Many Pallets Fit in an ISO Container?
Pallet capacity depends on which pallet, because container widths were set around imperial measurements rather than European pallet dimensions.
A Euro pallet measures 1200 × 800 mm. Loaded into a standard container, roughly 11 fit in a 20ft and 25 in a 40ft. Industrial pallets at 1200 × 1000 mm take more floor area, dropping capacity to around 10 in a 20ft and 21 in a 40ft. Exact counts shift with loading pattern and whether the pallets stack.
Neither figure represents a clean fit. Standard container width leaves unusable space alongside Euro pallets, and across thousands of movements that wasted width adds up — which is why pallet-wide containers were introduced on European routes.
Once a container is unpacked at the warehouse, its contents stop being container freight and become palletised road freight moving as individual consignments. Go Trans arranges pallet delivery across Europe for goods at that stage of the journey.
What Happens to a Container After It Arrives at Port?
The sequence runs the same way at every European terminal. The vessel discharges, customs clears the container, the shipping line releases it, a truck collects it from the terminal gate, and it travels to the first inland point for unpacking.
That collection leg is drayage in freight shipping — the short road movement between terminal and warehouse, booked separately from the ocean leg and priced on its own terms. It is the point at which a sea shipment becomes a road movement.
The container itself never belongs to the importer. It stays the shipping line's asset throughout, which is why the empty goes back to a nominated depot once unpacking finishes. Free time covers that round trip, and demurrage begins accumulating on any box still sitting at the terminal after the window closes.