Container Types: Flat Rack, Open Top, High Cube and When to Use Each

A buyer books a 40-foot open top for a machine that is 2,250 mm wide, because the inside width on the brochure says 2,340 mm. At the packing yard the crane lowers the machine and it jams against the roof frame: the opening at the top is narrower than the box below it. The load is re-booked on a flat rack, the shipment misses its vessel, and the invoice that follows carries over-width charges nobody had budgeted.

Picking between a standard box, a high cube, an open top and a flat rack is a measurement exercise, not a catalogue choice. Compare the cargo against the right dimension for each type, know which ones trigger out-of-gauge charges, and you can predict the freight bill and audit it line by line when it arrives.

• What this guide covers: dimensions and payloads for each container type from published owner specifications, how over-height and over-width are measured, and the US and Indian road limits that apply after the port.
• What it adds: a worked flat rack invoice audited in dollars and rupees, a gate re-measurement dispute traced hour by hour, and the booking data a transport system should refuse to accept without.

Same footprint, four jobs: standard, high cube, open top and flat rack

All four types share the ISO 40-foot footprint of 12,192 mm by 2,438 mm, so they stack and lock into the same cells, chassis and wagons. What changes is the height, how cargo goes in, and how much weight the frame is rated to carry, and those differences are large enough to change the freight bill.

The table mixes sources on purpose. ONE publishes its brochure figures in centimetres, converted here, and units in any fleet vary by build series; Triton's sheets say dimensions follow ISO standards within production tolerances. Two 40-foot flat racks in the table differ by more than 8 tonnes of payload, which is exactly why a booking must name the unit's rating, not just the type.

High cube boxes: 305 mm of extra height for nearly the same payload

A high cube is a standard box made one foot taller. On Triton's sheets the inside height rises from 2,393 mm to 2,698 mm and the door from 2,280 mm to 2,585 mm, while the payload falls only 160 kg, so a high cube is the default whenever cargo is light and bulky.

• Cubic gain: inside capacity rises from 67.7 m³ to 76.4 m³, about 12.9% more space for the same footprint.
• Door height rule: what fits is limited by the 2,585 mm door opening, not the 2,698 mm inside height; tall crates need clearance for forklift tines and floor bearers too.
• Pallet stacking: the extra 305 mm often allows a second tier of pallets that would not fit in a standard box, which is where most of the cost saving comes from.
• Road height: the box itself is 2,896 mm tall, so the chassis deck height decides whether the loaded vehicle stays within legal height on every road leg.

For cargo that weighs out before it cubes out, a high cube adds nothing and may cost more. The trailer and container cube utilization guide shows how to find which limit binds first, and the FCL versus LCL comparison covers when a part-load is cheaper than a whole box.

High cube dry containers on a lessor's published 40-foot specification give 2,585 mm of door height against 2,280 mm for the standard box, and 76.4 m³ against 67.7 m³ of capacity, for a payload only 160 kg lower; booking teams should therefore default bulky, light cargo to high cubes before considering special equipment.

Open tops: the roof opening, not the inside width, limits the load

An open top replaces the steel roof with removable roof bows and a tarpaulin so cargo can be lowered by crane. The usable width for a crane lift is the roof opening, which on ONE's 40-foot open top is 2,180 mm against an inside width of 2,340 mm.

• Top-loading width: anything wider than the roof opening must go in through the doors instead, where the opening is 2,330 by 2,240 mm on the same unit.
• Swinging door header: many open tops have a removable or hinged header above the doors, so tall cargo can be pushed in from the end once the header is swung clear.
• Over-height with a tent: cargo that rises above the roof line can sail with the tarpaulin tented over it, but it is then out of gauge and priced as such.
• Payload trade-off: the open top in the table carries 26,600 kg against 28,960 kg for the standard box, so dense cargo may hit the weight limit first.

The open top is the right box for in-gauge cargo that cannot be forklifted through the doors: glass crates, coils of cable on drums, stone blocks or machinery that must be slung. When the cargo is wider than the roof opening, or much taller than the box, it belongs on a flat rack instead, and the pricing logic changes completely.

Flat racks: ratings that differ by owner and cargo that overhangs

A flat rack is a floor with end walls, which may be fixed or fold down, and lashing rings along the sides. It carries cargo too heavy, too wide or too tall for a closed box, and its payload rating varies more between owners than any other type.

ONE's brochure lists its standard 40-foot flat rack at a 45,000 kg rating with 38,800 kg payload, and its high cube flat rack at 58,600 kg with 52,500 kg payload. Triton's flush folding unit is rated 52,500 kg with 47,260 kg payload. The safety approval plate fitted under the International Convention for Safe Containers carries each unit's approved data, and that plate, not a type average, is what the booking should match.

• Floor height: the deck sits well above the bottom of the corner castings; on Triton's unit the external height of 2,591 mm less 1,959 mm of inside height leaves about 632 mm, which counts toward any over-height calculation.
• Weight spread: heavy items with small feet need timber or steel bearers to spread the load across cross members; ask the owner for the unit's concentrated load guidance before stowing.
• Breakbulk use: ONE describes its breakbulk service as very large cargo carried on several flat racks laid together, used for items like yachts and factory components.
• Empty repositioning: folding end walls let empty racks stack, which is why owners prefer them and why availability at inland depots can be thin.

Flat rack payloads in published owner specifications range from 38,800 kg to 52,500 kg for 40-foot units, so a transport management system should store the rating from each unit's CSC safety approval plate and reject a booking whose cargo, lashing and dunnage exceed that figure, instead of trusting a generic flat rack type code.

Measuring out-of-gauge cargo and the lost-slot arithmetic

Cargo is out of gauge when it extends beyond the container's external envelope: wider than 2,438 mm or taller than the box's nominal height once it sits on the floor. Carriers then charge for the vessel slots the overhang blocks, so every millimetre should be measured and recorded by a named person.

ONE's brochure separates in-gauge special cargo, which stays within a flat rack's or open top's dimensions, from out-of-gauge cargo, which exceeds their width or height. Carrier tariffs and service contracts then convert the overhang into lost slots, usually one above for over-height and one each side for over-width, and the exact rule is in each carrier's tariff, not in any standard.

Out-of-gauge measures for cargo on a flat rack (all in mm)

  OH      = max(0, h_floor + H_cargo - H_box)
  OW_left = max(0, W_left_edge_overhang)      measured from the side rail
  OW_right= max(0, W_right_edge_overhang)
  For cargo centred on the rack: OW_side = max(0, (W_cargo - 2438) / 2)
  OL      = max(0, L_cargo - L_rack_internal)  over-length beyond end walls

  h_floor = H_box - H_inside   (deck height above the bottom castings)
  H_box   = 2591 (8 ft 6 in unit) or 2896 (9 ft 6 in unit)

  Road height on the trailer:
  H_road  = h_deck + h_floor + H_cargo

Example: press frame 2750 wide, 2300 tall on a rack with H_inside = 1959
  h_floor = 2591 - 1959 = 632
  OH      = 632 + 2300 - 2591 = 341
  OW_side = (2750 - 2438) / 2 = 156 each side

The same example on a high cube flat rack gives a floor about 636 mm high (2,896 less 2,260) and a cargo top at 2,936 mm, still 40 mm over a 2,896 mm box. A switch of equipment that looks like a fix on paper therefore saves nothing; only lowering the cargo, such as by removing a detachable part, would bring it into gauge.

The verified gross mass rule under SOLAS chapter VI regulation 2 applies to flat racks and open tops like any other packed container. IMO's guidance lets the shipper weigh the packed unit or add up cargo, packing, dunnage and securing material plus the tare; on a flat rack the lashing chains and timber can add hundreds of kilograms, so leaving them out understates the declared mass.

After the terminal gate: US and Indian road limits for awkward boxes

An over-width flat rack is legal on a ship once the carrier accepts it, but the truck carrying it must also meet road rules. Width is the usual trigger: cargo wider than the national limit needs a permit in both countries, and height depends on the trailer.

• US width: under 23 CFR 658.15, states may not impose a width limit of more or less than 102 inches, about 2,591 mm, on the National Network; wider loads need a state special-use permit.
• US height: the federal size rules in 23 CFR part 658 set no height limit, so each state on the route decides, and route surveys must check bridges and wires.
• India width: rule 93(1) of the Central Motor Vehicles Rules, 1989 limits overall width to 2.6 metres, and rule 93(8) bars loads extending laterally beyond the side of the body.
• India height: rule 93(4)(iii) allows 4.52 metres for a laden trailer carrying an ISO series 1 freight container, so the trailer deck height must be subtracted before judging any over-height cargo.

Indian road moves of flat rack cargo must respect Central Motor Vehicles Rules 1989 rule 93, which caps width at 2.6 metres and container-trailer height at 4.52 metres; a 2,750 mm wide press frame therefore needs over-dimensional cargo permission, while the US National Network allows 102 inches before a state permit is required.

Permits, escorts, route surveys and hydraulic trailers for very heavy pieces are covered in the guide to heavy-haul and over-dimensional cargo route surveys. That page deals with the road move; this one stops at choosing the container and checking the freight bill it produces.

Auditing a flat rack freight invoice in dollars and rupees

A flat rack invoice has more lines than a dry box invoice and more places for duplication. Audit each line against the booking, the measured overhang and the rate agreement, and expect to find the same service billed by two parties.

The two invoices below are illustrative. The US case is an import of the 2,750 mm wide, 2,300 mm tall press frame on a 40-foot flat rack, billed in dollars. The Indian case is an export of a 2,640 mm wide, 2,250 mm tall rolling-mill housing from a plant near Pune through Nhava Sheva, billed in rupees with ocean freight converted at ₹88 to the dollar. GST on Indian services is excluded.

The surcharges are the largest lines and the hardest to challenge, because they follow the measured overhang. The savings come from duplicated services, which is why the audit needs the lashing contractor's invoice and the terminal tariff side by side. A carrier's over-width charge for both sides is correct for centred cargo; for cargo offset to one side, the audit should ask for the measured overhang on each side separately.

A press frame re-measured at the gate: tracing a surcharge dispute

Surcharge disputes usually begin when the booked dimensions and the measured ones disagree and nobody can prove which is right. This trace follows the US import case from origin; times, numbers and transaction codes are illustrative.

1. Day 1, 08:30, booking: the forwarder books flat rack 40FR under booking BKG-55190 with cargo width 2,700 mm and height 2,300 mm from an old drawing, giving 131 mm over-width each side.
2. Day 6, 14:05, packing yard: after lashing, the frame sits slightly off-centre; the yard measures 2,750 mm overall with 176 mm overhang on the left and 136 mm on the right, but records only the total in an email.
3. Day 7, 10:20, terminal gate: the gate check records 2,760 mm and flags a dimension change. The carrier's special cargo desk re-checks stowage under amendment AMD-02 and confirms the slot plan the same day.
4. Day 31, 16:40, freight audit: the invoice shows the over-width charge at the higher measured width and a $750 equipment premium. The shipper's audit team has the booking width but no photographs, so it cannot dispute the width.
5. Day 38, 11:00, settlement: the premium is credited because the rate agreement covers it, but the width-based charge stands. The shipper adds a rule that a signed overhang sheet with photos must exist before any out-of-gauge box gates in.

Booking checks a TMS can enforce and judgment the project desk keeps

Dimension and weight checks are arithmetic and belong in fixed system rules. Judgement stays with people where the question is physical: whether a lashing plan is sound, whether a crane can reach, or whether a part can be removed to bring cargo into gauge.

Equipment checklist for the next oversized or crane-loaded shipment

Choose the least special box that physically fits, because each step from dry to high cube to open top to flat rack adds cost, availability risk and paperwork. Run the checks below in order and stop at the first type that passes.

Freight buyers who move special equipment regularly should hold unit ratings, drawings, measured overhangs and invoices in one record, so the audit in this guide takes minutes rather than weeks. If you are scoping a system to do that, you can share your requirements with us, and the logistics and supply chain library covers neighbouring container, freight and customs topics.