A flat rack is the container for cargo too wide, too tall or too heavy for a standard box: machinery, equipment, steel structures, large pipes. This guide covers how it is built, actual carrier specifications and what to check before booking.
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What is a flat rack?
A flat rack is a container with a floor and two end walls, but no side walls and no roof. It is made of steel and usually comes in 20' and 40' sizes, with collapsible or fixed end walls.
With no sides or roof, cargo is lifted in from above or loaded from the sides and lashed directly to the floor. Cargo may overhang the sides or top; the shipment then becomes out-of-gauge (OOG) cargo.
Flat rack dimensions and payload
The figures below are example specifications published by Hapag-Lloyd for its fleet. Actual units vary by manufacturer, age and owner, so confirm the unit you will receive with the carrier.
| Specification | 20' flat rack | 40' flat rack high cube |
|---|---|---|
| Inside length (between end walls) | 5.638 m | 11.652 m |
| Inside width | 2.194 m | 2.245 m |
| End wall height | 2.233 m | 2.265 m |
| Floor height | 0.37 m | 0.648 m |
| Max payload | 42.1 t | 49.1 t |
Compared with standard containers (20GP max payload 28.13 t, 40GP 28.75 t from the same source), a flat rack takes far more weight. That is why flat racks are often chosen for heavy pieces even when the dimensions would fit a standard box. Max payload assumes an evenly spread load; heavy pieces on a small footprint need floor load checks and dunnage.
When should you use a flat rack?
- The piece is wider than a standard container door (about 2.34 m) or an open top roof opening (about 2.23 m).
- The piece is both wide and tall, or shaped so it cannot pass through the doors.
- The piece is heavier than the payload of standard and open top containers (about 28.75 t to 30.05 t) but within the flat rack payload.
- It has to be lifted in from above or loaded from the sides.
When is a flat rack the wrong choice?
- The piece is longer than a 40' flat rack (about 11.652 m) or heavier than its payload: it usually ships as breakbulk, stowed directly in the hold or on deck.
- The cargo needs weather protection and still fits an open top: the tarpaulin-covered open top is usually the better choice.
- The cargo is light and fits a standard container: a standard box gives the best rates and schedules.
Why out-of-gauge cargo on a flat rack costs more
When cargo overhangs the sides or top, the neighbouring and upper container slots cannot be used. Carriers charge extra to cover these lost slots and must approve the booking in advance. Send dimensions, weight, centre of gravity and the lashing plan early so the carrier can plan stowage.
The road leg in Vietnam
When a flat rack with oversized cargo moves by road, height and width apply to the whole loaded vehicle. A container carrier over 4.35 m high, or any vehicle over 2.5 m wide, is oversize and needs a circulation permit under Circular 12/2025/TT‑BXD (as amended by Circular 19/2026/TT‑BXD).
Checklist before booking a flat rack
- Overall dimensions of the piece (including crates and protruding parts) and weight
- Centre of gravity, lifting points and lashing points
- Overhang on each side and on top (if any) so the carrier can plan space
- Road route from factory to port and from port to site
