Carton Cube, Mass Limit and Door Height Before You Book a Box

Volume is the first number a bulk order is measured by, and it is the one most often read too optimistically. A carton that travels cleanly inside a parcel lane stops being the unit of account the moment the order leaves as a full box. What an ocean booking is then built from is the stacked cube of the packing, the mass ceiling of the equipment chosen, and the height of the door everything has to pass through.

Key facts

• Published cube is not loadable cube. Dry-box internal volumes commonly quoted for a 20GP, a 40GP and a 40HQ sit near 33, 67 and 76 cubic metres; the planning figure we work from is lower, because blocking, dunnage and an imperfect stack consume part of the space.
• Mass can close a box before volume does. Dense cargo reaches its gross allowance first, so a load that fits on paper can be refused at the scale and the shorter box becomes the right answer.
• The packing list comes before the booking. Box count, outer sizes and gross weights are the inputs the selection is computed from; a slot reserved against guessed cartons is re-worked when actuals are measured at the dock.

What each of the three numbers decides

Three readings, taken in different places, decide which equipment a shipment goes on, and each rules something out rather than something in. The stacked cube decides whether the cargo fits at all, computed from the outer dimensions of every carton and pallet in the order rather than from the product sizes on a listing page. The maximum gross mass decides whether a load that fits can be lifted: it is fixed by the equipment and by road rules at both ends, and it does not move because the box looks half empty. The door opening decides whether the pieces get in, because interior height and door height differ by a few centimetres, and a pallet built to one and not the other becomes a re-packing job. A high-cube box buys vertical space; its floor length matches the standard box of the same nominal size.

Where the cube comes from

The arithmetic is short enough to do by hand and worth doing before anything is booked: multiply outer length, width and height in metres for one carton, multiply by the count, then add the loss you expect from the stack. A carton measuring 60 by 40 by 35 centimetres occupies roughly 0.084 cubic metres, so one hundred and twenty of them are about 10 cubic metres of pure packing.

The stack you can physically build is larger than the sum of the boxes, because part loads leave gaps at the top of each tier and mixed sizes cannot be column-stacked. A pallet adds its own height underneath the cargo, and unless it is racked its footprint cannot be shared with another SKU in the same tier. That is why a mixed order is planned differently from a single-SKU order of identical weight.

Nominal cube, practical cube, and the mass limit

Below is the comparison we use when a carton list arrives with a question about which box to take. The published column is nominal internal volume as it appears in carrier literature; the planning column is what a real stacking job usually leaves usable after the losses above.

Both columns are planning figures, typical rather than promised, and the operator's own specification governs where they disagree. The usual mistake in a first bulk order is choosing by volume alone: tile, paper, cast metal, bottled liquid and battery packs are high in mass for the space they occupy and reach the gross figure while the interior still looks under-filled, which is a refusal at the terminal rather than a negotiation.

What the packing must arrive with, and where this stops

Before a box selection means anything, the measurement behind it has to be trustworthy. Outer dimensions and gross weight belong on every carton line of the packing list, so the dock reconciles what it measures rather than assumes it. Pallet height is stated with the pallet in it, plus whether the load is stackable. Mixed cartons are declared with an explicit contents list, because a mixed tier breaks the column stack. Timber is counted separately, since a crate or pallet adds its own cube and brings marking obligations that sit with the treatment facility rather than with us.

Goods arriving at the wrong intake floor cost time: the routing ruling dated 2026-10-23 sends single-parcel B2C stock to Dongguan, palletised and crated B2B cargo to Shenzhen and Yangtze-delta consolidations to Suzhou across 24,000 square metres, and a lane departing Guangdong still needs a Guangdong intake. None of this is a rate argument; we publish no rate card, and the lane terms a box selection feeds are on the sea and air DDP lane page. The method also stops applying to three jobs: single-parcel orders measured by chargeable weight, groupage limited by a consolidator's cut-off calendar, and any piece exceeding the door opening, which is a lift-and-route question rather than a cube one. Terms of carriage are unchanged here and sit on the liability and compensation page; the three sites are on our company page.

Frequently asked questions

How many cubic metres does a 20GP or 40HQ really take?

Carrier literature commonly states nominal internal volumes near 33 cubic metres for a 20GP, 67 for a 40GP and 76 for a 40HQ, and most quotations are written against those figures. The volume a real shipment leaves usable is lower, because blocking, dunnage, part tiers and mixed carton sizes consume space the nominal figure assumes is free. We plan against the practical figure and confirm it against the operator's specification before booking.

Can a heavy order still take the shorter container?

Dense cargo usually does take the shorter box, and volume is the reason it is chosen last rather than first. Tile, paper, cast metal, bottled goods and battery packs reach the maximum gross mass for the equipment while the interior still looks under-filled, and a load over that mass is refused at the terminal rather than argued about. Cube and mass have to be compared together, which is why a carton list without weights cannot support a box selection.

What must a packing list contain before a container is booked?

It has to carry numbers the dock can check rather than numbers a listing page advertises, or the booking is rebuilt after the goods arrive. That means carton count with outer length, width and height plus gross weight on every line, pallet heights that include the pallet itself, a statement of whether each load is stackable, an explicit contents list for mixed cartons, and timber called out separately because crates and pallets add their own cube and their own marking obligations.

Sources and update note

Reviewed 2026-10-29. Nominal volumes and the internal-versus-door distinction were cross-checked against ONE container information and MightyShipping container sizes and load calculation. The planning column is our own working figure and is approximate. The intake routing rule and the 24,000 square metre floor total are this site's published parameters as of the review date, subject to confirmation at booking.

Published by SBT FulfillDock, the forwarding name under which Shenzhen Shibotong International Logistics Co., Ltd. trades.