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, and that is exactly backwards. ISO 668 defines the figures in millimetres and the foot labels are nicknames: the width is 2,438 mm, which happens to be 8 ft to within a millimetre, and a 40 ft box is 12,192 mm — precisely 40 × 304.8 mm, because the international foot itself is defined as 0.3048 m.

The one genuine exception is length. A 20 ft container is 6,058 mm, not 6,096 mm, because a 38 mm gap at each end lets two of them sit in a 40 ft slot with the twistlock spacing intact. That is why two 20 ft boxes measure 12,116 mm plus gaps rather than exactly 12,192 mm, and 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, and it is the one place where the numbers are authoritative for that specific box rather than for its class. Dimensions there are metric, weights are in kilograms with pounds underneath, and the figures are the ones 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 quotes typical values and says so.

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 road limits in much of Europe sit at 4.0 m total — with a 1.1 m chassis deck the box arrives 4.0 m tall exactly, so rounding the container to 2.9 m hides a clearance problem rather than revealing one.

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 is 7 ft 10.2 in, which most tables print as 7′10″. Stack that rounding across a three-tier load plan and the accumulated 15 mm can be the difference between the roof closing and not. The converter above always shows the exact decimal alongside the feet-and-inches form for this reason.