How this instrument works
Shipping containers come in a small set of standardized sizes so that ships, cranes, trucks and rail cars anywhere in the world can be built to handle them interchangeably. ISO 668, currently in its 2020 edition, is the international standard that defines this 'Series 1' family of freight containers — their external dimensions, weight ratings, and the minimum internal and door-opening dimensions manufacturers have to meet.
The number that actually matters for loading cargo is the internal dimension, not the external one — the walls, insulation and corrugated steel of the container eat into the space you can actually pack. A '40 foot' container isn't internally 40 feet long; ISO 668 puts a standard 40ft container's internal length at 11.998m, a little under the external 12.192m (40ft) the name refers to. This instrument returns those internal figures directly, which is what you need for cargo planning, not the marketing-friendly external size printed on the door.
'High-cube' containers share the same length and width as their standard counterparts but stand taller — an extra 305mm (about a foot) of internal height, aimed at cargo that runs out of headroom before it runs out of floor space. Container width, notably, doesn't vary across any of the four common types covered here: every one of them has a 2.330m internal width, since the industry standardized on a single width early on to keep pallet and rail-gauge compatibility simple.
- Choose a container type from the dropdown: 20ft standard, 40ft standard, 40ft high-cube, or 20ft high-cube.
- Read Internal length (m) — the usable length inside the container walls.
- Read Internal width (m) — 2.330m for all four types listed.
- Read Internal height (m) — 2.350m for standard containers, 2.655m for high-cube.
- Multiply length × width × height for a rough internal volume estimate, keeping in mind real loadable volume is always a bit less once pallets, dunnage and door swing are accounted for.
Worked example — a 40ft standard container
Select '40 ft standard' from the container-type list. ISO 668:2020 puts this container's internal dimensions at 11.998m long, 2.330m wide, and 2.350m tall — the numbers a freight forwarder or warehouse planner actually loads cargo against, not the 12.192m x 2.438m x 2.591m external dimensions the '40 foot' name is based on.
Multiplying those three figures gives a rough gross internal volume of 11.998 × 2.330 × 2.350 = about 65.7 cubic meters. Real usable volume for palletized cargo runs meaningfully lower than that once you account for pallet footprint inefficiency, bracing, and the fact that door-end space is rarely packed to the ceiling — a common industry rule of thumb treats 60-70 cubic meters of realistic capacity as the practical ceiling for a 40ft standard box, in line with this figure.
Questions
What are the internal dimensions of a 40ft shipping container?
Per ISO 668:2020, a 40ft standard container has internal dimensions of 11.998m long, 2.330m wide, and 2.350m tall. That's noticeably less than the 12.192m x 2.438m x 2.591m external dimensions the '40 foot' label refers to — roughly 194mm of length, 108mm of width and 241mm of height are lost to the container's own walls, floor and roof structure.
What's the difference between a standard and a high-cube container?
Height, and only height. A high-cube container shares the exact same internal length and 2.330m width as its standard counterpart of the same footprint, but stands about 305mm (roughly a foot) taller inside — 2.655m versus 2.350m. High-cubes are chosen for cargo that's bulky or needs extra stacking headroom rather than more floor footprint, such as machinery, furniture, or goods on tall pallets.
Why is container width always 2.330m internally?
Because the shipping industry standardized on a single external width — 2.438m (8 feet) — across essentially every common Series 1 container type, and that external width, minus a consistent wall thickness, produces the same 2.330m internal width regardless of length or height variant. Keeping width fixed simplifies handling equipment, ship-hold cell guides, and rail and road clearance rules, all of which are built around one width figure rather than several.
Is a 20ft container exactly half a 40ft container?
Close, but not exact. ISO 668:2020 puts a 20ft standard container's internal length at 5.867m, while a 40ft standard container's is 11.998m — 5.867 × 2 = 11.734m, about 264mm short of the actual 40ft figure. The two sizes share the same standardized internal width (2.330m) and height (2.350m), so a 40ft container isn't literally two 20ft containers end to end; it's a separately specified length in the same ISO 668 family.
Does the internal volume from length x width x height equal the container's real loading capacity?
Not quite — it's a useful upper bound, not the practical figure. Multiplying the three internal dimensions gives the container's gross internal (cube) volume, but real cargo rarely uses 100% of that space: pallets leave gaps, cargo has to clear the door swing, and irregular loads waste corners. Freight planners typically apply a fill-efficiency factor well under 100% to this cube figure to estimate realistic loadable volume.