Shipping Container Dimensions: Only the Outside Is Standard

The external length of a 40ft container is 12,192 mm. That figure is written into ISO 668, and its tolerance runs one way only — a box may be 10 mm short of it, never a millimetre over. The internal length appears nowhere in the standard as a number.

Short answer: a 20ft DC measures 5.90 x 2.35 x 2.39 m inside (33.2 m3), a 40ft DC 12.03 x 2.35 x 2.39 m (67.7 m3), a 40ft high cube 12.03 x 2.35 x 2.70 m (76.3 m3) and a 45ft high cube 13.56 x 2.35 x 2.70 m (86.0 m3). Those are industry-typical values. What ISO guarantees is a floor beneath them, not the numbers themselves.

That single sentence is the whole problem with container dimensions: the outside is standardised, the inside is not, and for weight there is not one ceiling but three. Below is each figure, where it comes from, and which one actually binds.

Master Table: Dry Container Dimensions

And the same five boxes by weight

Why the External Dimension Is Not the Internal One

Container names (20ft, 40ft, 45ft) describe the external length fixed by ISO 668. The internal dimension is what remains after the corrugation depth, corner castings, floor structure and roof bows are deducted. Where the loss goes differs by axis — and, surprisingly, is identical on every size:

The relationship between 20ft and 40ft is no accident either. Shorter containers are deliberately built short of their nominal foot length so that two of them, with a 76 mm gap between, occupy exactly one 40ft slot:

2 x 6,058 mm + 76 mm = 12,192 mm  (two 20ft = one 40ft slot)
4 x 2,991 mm + 3 x 76 mm = 12,192 mm  (four 10ft)
9,125 mm + 2,991 mm + 76 mm = 12,192 mm  (one 30ft + one 10ft)

Which yields a practical warning: a 20ft container is not 6.096 m long. The literal conversion of 20 feet is 38 mm longer than any real box — and those 38 mm are exactly half the 76 mm module gap. It is the single most common numerical error in loading calculations, and it doubles when two 20ft units are treated as one 40ft slot.

On internal dimensions, all ISO says is a floor: internal dimensions shall be "as large as possible" but in any case not less than the Table 3 values — 11,998 mm of length on a 40ft, 2,330 mm of width, and "nominal external height minus 241 mm". Real boxes beat that floor by 3-4 cm. Which is why there is no single standard figure for "the internal length of a 40ft"; Hapag-Lloyd alone publishes three different internal widths across its own 40ft HC series. Use the ISO minimum when you need a guaranteed-fit check, and the carrier's equipment card when you need a utilisation figure.

The Dimension Nobody Checks: The Door Opening

However large the internal cube, if the cargo will not pass the doors the container is no use to you. The door opening is always smaller than the internal section, and the loss is asymmetric: almost nothing across the width, a lot in height.

High Cube: The Economics of 31 Centimetres

The only difference between a 40ft HC and a 40ft DC is internal height: 2.70 m against 2.39 m. The floor is identical — which is why the number of pallets on the floor does not change.

For light, bulky goods — textiles, furniture, packaging, plastics, toys — not booking a high cube is a straight capacity loss. For dense goods — ceramics, glass, metal, chemicals — it buys nothing at all: those loads hit the weight ceiling long before the cube fills, and the high cube's extra 150 kg of tare actually costs you payload.

Reefer: The Most Misleading Box on the Card

In a refrigerated container two losses stack: the machinery pack in the front wall, and polyurethane insulation on every surface. The result is close to ten cubic metres of difference between two boxes that look identical from outside.

The insulation is thinner than the internet believes: 80 mm in the roof, 63.5 mm in the side walls, 74 mm in the door panels. The widely repeated "200 mm of insulation" cannot be true — with 2,280 mm of internal width inside a 2,438 mm shell there are only 79 mm per side to work with, steel skins included.

Open Top, Flat Rack and Hardtop: Dimensions for Out-of-Gauge

The 30-54 tonne spread in flat rack payload is not measurement noise but different frame classes: 34 / 40 / 45 t gross on 20ft units and 50 / 55 / 60 t on 40ft high cubes. Those ratings also assume the load is spread along the full length of the side rails; a short, concentrated load reduces the permissible weight according to the manufacturer's loading chart. Anything above 30 t comes from a limited "heavy tested" sub-fleet and can run into terminal restrictions, so it has to be booked specifically.

A Real Decision: Machined Castings from Felixstowe to Newark

A UK engineering supplier ships to New Jersey: 20 industrial pallets, each 120 x 100 x 95 cm and 1,300 kg gross — machined castings and gearbox housings. That is 26,000 kg and 22.8 m3. Because the pieces are bulky on the pallet, the shipper books a 40ft high cube out of habit.

Run the density first: 26,000 kg in 22.8 m3 is 1,140 kg/m3, three times the 375 kg/m3 at which a 40ft high cube weighs out. Everything follows from that. The 76.3 m3 container ends up 29.9% full by volume — three quarters of the cube is air — while sitting at 90.9% of its 28,600 kg payload. The first image above is exactly this plan, computed in CargoDuo.

The decision is now obvious: 26 tonnes of castings fit one container but not one truck. The high cube's extra 8.6 m3 does nothing for this load, and its higher tare costs 150 kg of payload. Splitting into two 20ft boxes raises the volume fill to 34.4%, puts each combination around 56,000 lb, and removes the permit, the axle problem and the routing constraint in one move.

Tare, Payload, Max Gross and VGM: Four Numbers, Four Meanings

A packed container without a VGM cannot be loaded aboard. That has been the rule under SOLAS Chapter VI Regulation 2 since 1 July 2016, and the responsibility sits with the shipper named on the bill of lading — it cannot be delegated. Two methods are permitted: Method 1 weighs the packed container, Method 2 adds up the weights of everything inside plus the tare. Method 2 is not freely available: it must be certified and approved by the national authority where the container was packed, and several countries restrict it to authorised economic operators.

One widespread misunderstanding worth killing: the SOLAS text contains no tolerance at all. The ±5% quoted around the industry is a national enforcement threshold, not an accuracy allowance — the UK's MGN 534 states it will be applied "on a case by case basis" — and it does not soften the shipper's duty to determine the mass as accurately as possible. If the terminal reweighs, the terminal's figure is the one that stands.

Quick Picker

The Road Leg: Where the Dimensions Actually Bite

At sea container dimensions are standard. The moment the box leaves the terminal, national road law takes over — and it constrains a different axis on each side of the Atlantic.

The scale of it: the Port of Los Angeles alone handled 10,239,318 TEU in calendar year 2025 — only the third time in its 118-year history that it has passed ten million. Every one of those boxes eventually meets a chassis, a bridge formula and a state height limit.

Conclusion: The Dimension Table Is a Starting Point, Not a Decision

Knowing container dimensions is necessary but not sufficient. The external dimension is standardised and not up for debate; the internal one moves a few centimetres by carrier, series and build year; the door opening is 11-12 cm shorter than the interior; and on weight the equipment card, the CSC plate and road law set three independent ceilings. The real question is different: in what arrangement, with what weight distribution and in how many trips does your cargo fit inside those dimensions?

Frequently Asked Questions

External dimensions, tolerances and minimum internal dimensions are from ISO 668:2020 (including Amd 1:2022, which raised the rating for all 20/30/40/45 ft classes to 36,000 kg) and ISO 1496-1:2013 — note that ISO 668:2020 is at stage 90.92, "International Standard to be revised", so an eighth edition is in the pipeline; internal dimensions, door openings, tare and payload from the published equipment specifications of Maersk, Hapag-Lloyd, CMA CGM, ONE and Evergreen; the weight markings on the door from ISO 6346; the contents of the CSC plate from Annex I of the 1972 International Convention for Safe Containers; the VGM obligation from SOLAS Chapter VI Regulation 2 and MSC.1/Circ.1475; US road limits from 23 U.S.C. § 127 and 23 CFR § 658; the 2025 throughput figure from the Port of Los Angeles. The 20-pallet arrangements and the 29.9% / 90.9% / 34.4% / 46.1% fill rates are real output from load plans run in CargoDuo. Internal dimensions in the tables are nominal and carry a manufacturing tolerance of ±10 mm; where millimetres matter, confirm the figures for the specific container with your carrier.