Unit Converter

8 ft = 2.438 m (universal container width) · 8′6″ = 2.591 m (standard height) · 9′6″ = 2.896 m (high cube height) · 20 ft = 6.058 m and 40 ft = 12.192 m external length. Full metric tables: container dimensions in meters.

Container sizes look like round imperial numbers that convert to awkward metric ones, but both are exact. ISO 668 (read in IS 6566:2001 and GOST R 53350-2009) gives every outside size in both units, and the sizes themselves are feet: its millimetre figures are the foot sizes rounded to the millimetre. The width is 2,438 mm, 8 ft (2,438.4 mm) rounded, and a 40 ft box is 12,192 mm — exactly 40 × 304.8 mm, because the international foot is defined as 0.3048 m.

The one genuine exception is length. A 20 ft container is 6,058 mm (19 ft 10½ in), not 6,096 mm: it is 38 mm shorter than a true 20 ft so that two of them, with a 76 mm (3 in) gap between them, take the slot of a 40 ft box and put their corner castings where its castings would be. Two 20 ft boxes add up to 12,116 mm, and with the gap to 12,192 mm, which is why the industry counts in TEU rather than in feet of steel.

The practical consequence for conversion: never round a container figure to a "nice" metric number. 8′6″ is 2.591 m, not 2.6 m — a 9 mm error that will not matter for a rough sketch but will matter when you are checking door clearance or a road-height limit.

Every container carries a CSC safety-approval plate on the left door, with its maximum gross and allowable stacking load in kilograms with pounds underneath; the tare and payload are not on it but in the weight block on the doors. Those door markings and the plate are the one place where the numbers are authoritative for that specific box rather than for its class, and they are the figures a terminal or a surveyor will act on.

Carrier spec sheets mix systems more freely: internal dimensions in millimetres, capacity in cubic metres with cubic feet in brackets, payload in kilograms and pounds. When two sources disagree by a few millimetres it is usually a build-year difference in the flooring or the door frame, not an error — which is why this site gives every figure with its status (set by the standard, printed by most sheets, or a range where they differ) and the sheets behind it.

Converting the other way, for construction work: 2,352 mm of internal width is 7 ft 8.6 in, so a nominal 8 ft sheet of plywood will not fit flat across a container interior. That single conversion decides more container-conversion layouts than any other.

The expensive mistakes in unit conversion are all rounding, and they cluster in three places. Height: a 9′6″ high cube is 2.896 m, and the road limit in much of Europe is 4.0 m overall, the height Directive 96/53/EC sets. On a low-bed chassis whose deck stands 1.1 m high unladen, as Schmitz Cargobull prints it, the box reaches 3.996 m, 4 mm inside the limit, so rounding the container to 2.9 m already uses up the whole margin and hides how close the load is.

Width for cargo planning: rounding 2,352 mm internal to 2.35 m is harmless, but rounding to 2.4 m invents 48 mm that do not exist and can turn a two-pallets-abreast plan into a one-pallet one at the door.

Feet-and-inches display: 2.393 m, the inside height of a standard box, is 7 ft 10.2 in, which most tables print as 7′10″ — 5 mm less. Repeat that rounding on each tier of a three-tier load plan and the 16 mm it adds up to can be the difference between the top tier fitting under the roof and not. The converter above always shows the exact decimal alongside the feet-and-inches form for this reason.