Why container sizes differ between sources

Of 137 container figures published by two or more sources, 103 disagree, weights far more than dimensions. We kept 570 of 628 transcribed values, and planning on the smallest published floor instead of the largest changes the pallet count in none of 110 pallet and container pairings.

By Oliver Bennett · Published 29 October 2026 · Data as of 27 October 2026, from spec sheets retrieved that day

Look up the inside length of a 40ft container on five websites and you may get five answers. None of them is necessarily wrong. Containers are built by different factories to a standard that fixes the outside and leaves the inside to the builder, and spec sheets round, convert and copy in different ways. PalletSpec keeps every published value and shows the spread rather than picking one.

How many sources stand behind each figure

Across the 16 container types there are 161 published figures with sources behind them. Of these, 24 rest on a single source, 66 on two, 39 on three and 32 on four or more. Of the 137 figures with at least two sources, 34 agree to the millimetre or kilogram; the other 103 differ.

Which figures vary most

Weights move far more than dimensions. Tare and payload depend on the steel, floor and fittings each builder chooses, and on the gross rating each owner puts on the plate. Inside dimensions are tighter because the outside is fixed by ISO 668 and walls are much the same thickness everywhere. The largest disagreement on an inside dimension of a closed box is the inside height of the 20ft open top: 2,348 mm to 2,380 mm, 32 mm apart.

The widest spreads

Flat racks and platforms dominate the list. Their designs differ by builder, with fixed or folding ends, different floor beams and different ratings, so a single type covers boxes that are really several products. Their ranges are kept as real variation rather than errors.

Values we did not use

Of 628 values transcribed from the source files, 570 were accepted and 58 left out. Each check is simple arithmetic or a comparison with the other sources:

Some examples. One carrier's 20ft dry sheet printed a tare in kilograms that did not match its own figure in pounds, so all its weights for that box were dropped. A forwarder gave the 20ft payload as 25,000 kg, more than 10% below the 28,330 kg on which three other sources agreed. One high cube reefer sheet printed a payload 1,000 kg higher than its gross minus its tare; we cannot tell which of the three numbers is wrong, so none is used. Another gave a reefer inside height whose length × width × height came out 5.4% below the volume on the same sheet; the height was dropped and the volume kept.

Why plans use the smallest size

Every load plan and planner result on PalletSpec uses the smallest published inside length and width, so that the count holds in whichever box turns up. That sounds costly, but the spreads are small enough that it never is. We packed every pallet standard into all 10 containers with a floor using the largest published inside size instead, and the count changed in none of the 110 pairings. Pallets come in steps of hundreds of millimetres, and a few millimetres of wall rarely decide a row.

Height is where the spread can matter. The 40ft high cube reefer is published at 2,537 mm to 2,552 mm inside; a unit that stacks two high in the tallest box may not in the lowest. The double stacking guide uses the lowest figure for that reason.

Reading a range

On each container page the typical value is the median of the accepted sources, and a small track shows every published value between the lowest and highest. A figure with one dot has a single source. If your shipment depends on a few millimetres or a few hundred kilograms, the plate on the door and the carrier's own sheet for that box are the figures that count. The full source list is under sources and method.

More guides: 20ft vs 40ft vs 40ft high cube containers · Shipping container door dimensions · Container weights: tare, payload and max gross · Reefer vs dry container: what the insulation costs · Open top vs flat rack vs platform containers · Pallet dimensions in inches · 48 ft vs 53 ft trailer · All guides