Flat rack container: what it is, dimensions and how it travels by road
Of all the container formats moving around the world, the flat rack is the one that exists for cargo that fits in none of the others. Machinery, vehicles, pipes, steel structures, transformers, boats: when a piece is too wide for the doors, too irregular for a closed box or simply too big, it travels lashed down on a flat rack. It is the basis of project cargo in sea freight and, on the road leg, the most frequent entry point into special transport.
This guide covers the equipment itself: what a flat rack is and what types exist, its dimensions and capacities in 20 and 40 feet, what cargo travels on it and how it is lashed. And then the part that decides budgets: when the combination of chassis, deck and cargo stops fitting within the general limits and moves into the special transport regime. If what you need is the road regime for oversized containers in general, or how to request a quote for a move of this kind, we have dedicated guides; this one is about the equipment.
What a flat rack container is, and what types exist
A flat rack is a container with no roof and no side walls: a high-strength steel deck with an end wall at either end, built on the same standard ISO corner castings as any other container. That dual nature is the key to everything else. For the ship, the terminal and the crane it is a container, lifted, stacked and stowed by its corner castings like any other box. For the cargo, it is a lashing platform open at the top and at the sides.
A flat rack is not a container with its walls missing: it is a lashing platform with ISO corners. Everything that does not fit in a closed box travels on it.
There are three main variants.
Fixed flat rack (welded end walls). The end walls are welded to the deck. This is the sturdiest version and the usual one for the heaviest cargo.
Collapsible flat rack. The end walls fold down onto the deck. Loaded, it works exactly like the fixed one; empty, it folds, and several collapsed flat racks stack and travel as a single unit. That is a real logistical advantage on the empty return, because it cuts trips and repositioning costs.
Platform, or bolster. The version with no end walls: just the deck and its corner castings. It is used for very long pieces, or when the geometry of the cargo leaves no room even for the end walls.
Dimensions and capacities: the reference table
The figures vary slightly by manufacturer, series and owner. Those below are the market reference; the specific unit is always checked against its own plate.
| Parameter | Flat rack 20' | Flat rack 40' |
|---|---|---|
| External length | 6.06 m | 12.19 m |
| Usable deck length | ~5.60–5.95 m | ~11.66–12.17 m |
| Usable deck width | ~2.20–2.40 m | ~2.35–2.40 m |
| Usable height at the end wall | ~2.20–2.30 m | ~1.95–2.28 m depending on series |
| Deck height (load floor) | ~0.37–0.40 m | ~0.63–0.65 m |
| Tare | ~2,500–3,000 kg | ~4,900–5,500 kg |
| Maximum payload | ~27,000–30,000 kg | ~39,000–45,000 kg depending on series |
| Lashing rings (typical capacity) | up to 2,000 kg per ring | up to 4,000 kg per ring |
Two rows of that table decide more operations than the rest. The first is the deck height: those 63–65 centimetres on the 40 foot (37–40 on the 20) travel underneath the cargo for the whole road leg and add a height the piece itself does not have. That is the reason cargo transfer exists. The second is payload against tare: a 40 foot flat rack takes a great deal of cargo, but it weighs close to 5 tonnes on its own, and that tare counts on the weighbridge for the whole road combination.
What travels on a flat rack
The flat rack is the format for cargo that does not fit in a closed box, and its real catalogue reads like an inventory of industry: construction and agricultural machinery, vehicles and tracked equipment, long pipes and profiles, steel structures and prefabricated sections, transformers and electrical equipment, large-diameter coils, boats on cradles, project pieces for industrial plants. Everything built large that travels by sea ends up lashed to one sooner or later.
The cargo is placed on the deck, with cradles, chocks or frames where the geometry calls for them, and lashed to the deck lashing rings, generally rated at a maximum of 2,000 kilos per ring on the 20 foot and 4,000 on the 40. Some 40 foot series also carry lashing winches with webbing straps. When the piece overhangs at the sides or on top, the flat rack still does its job, because that is what it is for: the cargo travels overhanging, declared out of gauge (OOG) for the vessel and the terminal, and with the road consequences set out below.
From ship to road: when a flat rack becomes special transport
Here is the turn that decides budgets. On the ship and in the terminal, a flat rack with overhanging cargo is an OOG unit: it takes up additional cells, it is stowed with clearance, it pays its surcharge, and there the matter ends. On the road there are no cells. There are circulation limits, and what gets measured is not the box but the combination — chassis, flat rack deck and cargo — as a single piece.
On the ship, a flat rack is one unit among many. On the road, what circulates is the combination: chassis, deck and cargo, measured as a single piece.
The general limits are those of Anexo IX del Reglamento General de Vehículos (RD 2822/1998): 2.55 metres in width, 4 metres in height and maximum masses of up to 44 tonnes depending on configuration. Cargo overhanging the sides of the flat rack exceeds the width easily; tall cargo, added to the 63–65 centimetre deck and to the chassis, comes close to the height limit or passes it. One point that is often missed: the height exception in Orden PJC/780/2025, the 4.5 metres for approved combined-transport containers, applies only to closed containers. It does not reach a flat rack with overhanging cargo, because the box is not closed and the excess is not produced by the container. Once any threshold is passed, the file moves to the ACC, the Autorización Complementaria de Circulación, with its categories: the generic one, quick; the specific one, with a drawing of the combination and prior notice of the journey; the exceptional one, with an itinerary study. It is issued by the Servei Català de Trànsit for roads in Catalonia, and by the DGT when the itinerary leaves Catalonia onto the state network.
The practical consequence for whoever plans the move: the same flat rack that crossed half the world as one more unit on the manifest needs, for its last kilometres, real measurements taken at the outermost points, a height and mass calculation for the combination and, depending on the result, an authorisation, a different trailer or a cargo transfer.
the guide to the road regime for oversized containers: open top, flat rack and high tonnage →
Lashing: rings, chains and who answers for it
On a flat rack the cargo travels lashed, and lashing has both its standard and its allocation of responsibility.
The technical standard is the EN 12195 series: calculation of braking and cornering forces, certified chains and tensioners, edge protection. It is enforceable in roadside inspections through Anexo III del Real Decreto 563/2017. The lashing rings on the deck set the capacity available at each point, which is why the lashing plan is calculated on the actual piece: weight, centre of gravity, usable lashing points.
Responsibility is allocated by artículo 20 de la LCTTM, as amended by RDL 3/2022: loading and stowage fall to the shipper unless agreed otherwise in writing before the vehicle is presented, and the carrier answers for inadequate stowage when it was carried out following its instructions. In flat rack practice that means one thing. Who lashes, with what, and on whose instructions goes in writing before the cargo moves. On export there is a second point: lashing for sea carriage is a service that is requested expressly in the enquiry, never an assumption.
How we approach it at Pastor
Sixty years of family tradition in special transport from the Port of Barcelona, where the flat rack is a regular part of the daily operation. Port procedures are resolved in advance, with registration in Portic and with the terminals inside the port area, and our own fleet of conventional low bed and extendable platform covers both the transport of the loaded flat rack and that of the transferred piece when height or mass call for it.
The work starts where it always starts: with measuring. From the dimensions of the cargo at its outermost points and the real weight, we calculate the combination in each possible configuration (flat rack on chassis, flat rack on platform, piece transferred onto low bed), resolve the authorisation category that matches each one and propose the simplest. Lashing is calculated to the EN 12195 standard on the actual rings of the unit, the allocation of responsibility is agreed in writing, and if the flat rack is collapsible the empty return is optimised: folded, stacked, one single trip.
For the freight forwarder and the shipper the result is the same promise as always: the box that crossed half the world without incident does not get complicated in its last kilometres. The shipper holds a single point of contact: ours.
the complete guide to special transport via the Port of Barcelona in 2026 →
Frequently asked questions
What is a flat rack container?
What is the difference between a fixed and a collapsible flat rack?
What are the dimensions and payload of a 40 foot flat rack?
12.19 metres of external length, with a usable deck of roughly 11.7–12.2 metres by 2.35–2.40 wide, a tare of about 5 tonnes and a payload of 39–45 tonnes depending on series. The deck puts the load floor at some 63–65 centimetres, a figure that matters more than it looks on the road leg.When does a flat rack require special transport by road?
2.55 metres in width, 4 metres in height or the maximum mass of the configuration. The 4.5 metre height exception covers only approved closed containers, not a flat rack with overhanging cargo. Once a threshold is passed an ACC is required, and sometimes the better answer is a cargo transfer.How is cargo lashed on a flat rack?
2,000 kilos per ring on the 20 foot and 4,000 on the 40, using certified chains, webbing and tensioners calculated to the EN 12195 series, with cradles or chocks wherever the geometry of the piece calls for them. The lashing plan is drawn up on the actual piece: weight, centre of gravity and usable lashing points.Do you have cargo for a flat rack — or a flat rack to move?
Send us the dimensions of the piece at its outermost points, the weight and the origin and destination. We calculate the combination, resolve the authorisation if one is needed and return the proposal within 24 working hours.
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