The volume a standard dry container can carry falls into two figures: the nominal capacity fixed by its internal dimensions, and the practical carton load that real cargo achieves. Both are tabulated below.
| Container | Nominal capacity | Practical carton load |
|---|---|---|
| 20ft Dry (20DC) | 33.2 m³ | ~25–28 CBM |
| 40ft Dry (40DC) | 67.7 m³ | ~52–58 CBM |
| 40ft High Cube (40HC) | 76.3 m³ | ~60–68 CBM |
The distance between the two columns is the substance of the problem. A quote or an order sized against the nominal figure assumes volume that rigid cargo cannot occupy, and the resulting shortfall is among the more costly recurring errors in ocean freight planning.
Deriving the Nominal Figure from ISO 668
Nominal capacity is the product of internal length, width, and height (full specifications appear on the container dimensions guide). Those internal dimensions follow from the ISO 668 container standard, so nominal capacities remain consistent across carriers. The full 67.7 CBM of a 40DC is unattainable with cartons: a carton is a rigid rectangle, and unless its dimensions divide evenly into the container's along every axis, unusable slices remain along the walls, beneath the ceiling, and at the door end.
The Four Variables Behind the Practical Load
1. Carton dimensions relative to the container. This is the dominant variable. A 60 × 40 × 40 cm carton loads a 40DC to about 71% (48 CBM) under orientation optimization; a marginally different carton reaches 80%+ in the same box solely because it tessellates more cleanly. No formula substitutes for the packing computation. The container loading calculator resolves the actual arrangement in the browser and renders the fit in 3D.
2. Rotation constraints. Cargo marked "this side up" cannot lay its height down as depth. Fixing orientation costs 3–10 percentage points of utilization.
3. Palletized versus floor-loaded. Pallets contribute their own footprint and height and seldom tile the floor exactly. Palletized loads settle at 50–60% volume utilization; floor-loaded cartons reach 70–85%. The gap — on the order of 10+ CBM in a 40ft — explains why high-volume, low-value cargo is frequently floor-loaded despite the added handling. See how many pallets fit in a container.
4. The weight ceiling. A 40DC's payload is ~28,800 kg and a 20DC's is ~28,200 kg. Dense cargo — tiles, hardware, canned goods — reaches the weight limit well before the volume limit: a 20DC is full at 28.2 tons even with two-thirds of its space still empty. The subject is developed in container weight limits and VGM; the VGM (verified gross mass) declaration is itself a SOLAS requirement administered by the IMO, and it applies to every packed container irrespective of fill level.
Practical CBM by Cargo Profile
| Cargo profile | 20DC | 40DC | 40HC |
|---|---|---|---|
| Uniform cartons, rotation allowed | 26–28 CBM | 52–58 | 62–68 |
| Uniform cartons, this-side-up | 24–26 | 52–55 | 58–63 |
| Palletized (EUR/GMA) | 18–22 | 38–45 | 42–50 |
| Mixed carton sizes (manual load) | 22–25 | 48–54 | 54–60 |
These figures are planning benchmarks rather than guarantees; the actual carton size should be run before booking.
Worked Case: 1,200 Cartons out of Shenzhen
Consider an FBA seller consolidating a season's stock in Shenzhen: 1,200 cartons of 50 × 35 × 30 cm at 7 kg each, which is 0.0525 CBM per carton, or 63 CBM and 8,400 kg in total. Measured against the nominal column, a 40DC (67.7 m³) appears to have room to spare. Measured against the practical column, it does not: a this-side-up carton load in a 40DC stows 52–55 CBM in practice, and even with free rotation the benchmark peaks near 58. The correct equipment is a 40HC, whose 60–68 CBM practical range encloses 63 — though a load this close to the top of a range is precisely the case where benchmarks give way to a computed stow.
Open this exact load in the container loading calculator
to see the 3D arrangement, or
run max-fill mode
to see how many of these cartons the 40HC takes at most.
The cost of the wrong choice follows directly. Had the seller booked the 40DC on the nominal figure, roughly 5–10 CBM of cartons would have been turned away at the origin warehouse. That remainder ordinarily moves as a separate LCL consignment — billed per revenue ton, carrying its own origin charges, documentation, and destination handling, and often routed onto a different vessel under a different customs entry. On most lanes the overflow shipment costs more on its own than the entire rate premium of the 40HC would have. The nominal-versus-practical gap is therefore not academic: it separates one clean container from a container plus an expensive orphan shipment.
Four Ways Capacity Is Miscounted
Quoting customers on nominal volume. A trader who promises "67 CBM per 40ft" to a buyer has committed to roughly 10 CBM that will not physically load. The shortfall either ships at the trader's expense or becomes a contract dispute.
Ignoring the payload ceiling on dense cargo. Ceramic tile at around 2,000 kg/m³ exhausts a 40DC's 28,800 kg payload at roughly 14–15 CBM — about a fifth of the nominal volume. Booking space by CBM for dense cargo overbuys volume and can trigger overweight penalties at the terminal or on the road leg.
Overlooking the door aperture. The door opening sits below the internal ceiling — about 228 cm high on a standard-height box and 257.7 cm on a 40HC. A pallet stacked to clear the 239 cm interior still will not pass the doors; pallet-height plans must work from the door figure, not the ceiling.
Counting pallet CBM in place of carton CBM. A packing list that sums loaded-pallet volumes double-counts the air between cartons and pallet edges. Capacity planning requires the carton CBM; the pallet CBM governs only LCL billing and warehouse storage.
Most of these are correctable through load design rather than a larger box — how to maximize container space covers the orientation, carton-size, and floor-versus-pallet decisions that recover real CBM without added freight spend.
Non-Standard Equipment and Marginal Losses
45ft High Cube. On some lanes a 45HC (86.1 m³ nominal) serves cargo that outgrows a 40HC; its availability and pricing vary far more than those of the standard three sizes.
Overheight and overlength pieces. Cargo that cannot clear the door aperture moves in open-top or flat-rack equipment, where CBM capacity ceases to be the binding constraint and lashing, gauge, and crane access govern instead.
Dunnage consumes volume. Airbags, edge protectors, and desiccant claim a small but genuine share of the stow — typically a percent or two — which becomes decisive when a load computes to fit near the top of a practical range.
Thresholds for the Next Size Up
Above ~26 CBM of real cargo — a 20DC is at risk; price a 40DC.
Above ~56 CBM — price a 40HC, which typically carries only a small premium over a 40DC while adding ~8.6 m³ of nominal space.
Above ~66 CBM — two containers, or a revised carton design.
Below roughly 13–15 CBM, FCL may not be justified at all; see FCL vs LCL for the break-even math.
How many CBM fit in a 40ft container?
Nominally 67.7 m³, but with real cartons expect 52–58 CBM (floor-loaded) or 38–45 CBM (palletized).
How many CBM fit in a 20ft container?
Nominally 33.2 m³; practically 25–28 CBM for floor-loaded cartons.
Why can't I use the full nominal volume?
Cartons don't tessellate perfectly into the container's internal dimensions, and rotation limits, pallets, and the payload weight ceiling all remove usable space.
Is a 40HC worth it over a 40DC?
Usually yes for light, bulky cargo: about 8.6 m³ more nominal volume for a small rate premium. For dense cargo that hits the weight limit first, the extra height buys nothing.
How many cartons fit in a 20ft container?
It depends entirely on carton size. At 60 × 40 × 40 cm (0.096 CBM each), a floor-loaded 20ft typically takes roughly 260–290 cartons — the 25–28 CBM practical range of its 33.2 m³ nominal volume.
Does a 40ft container hold twice as much as a 20ft?
By volume, slightly more than twice: 67.7 m³ vs 33.2 m³. By weight, no — payloads are nearly identical (28,800 kg vs 28,200 kg), so dense cargo that maxes out weight gains almost nothing from the bigger box.