Air Cargo Container (ULD) Sizes

A ULD is any device that lets loose cargo load as one unit into an aircraft’s cargo system: the hold floors carry powered rollers and locks that grip the ULD’s base, so a 1.5-tonne unit moves with a fingertip and stays put at 2.5 g. Two families exist. Containers (also called cans or pods) are closed aluminium boxes — rigid walls, a door of fabric or solid panel, and often a contoured profile that follows the fuselage curve. Pallets are flat aluminium sheets with seat-track rims; cargo is stacked on them, covered, and held by a rope net lashed to the rim, its contour built to match the hold it flies in.

The split is practical, not cosmetic. Containers protect cargo, load fast, and dominate lower-deck (belly) freight on passenger aircraft. Pallets take awkward and oversized pieces a can will not swallow, and dominate freighter main decks, where cargo can be stacked to 244 or even 300 cm under the crown of the fuselage. Both are certified aircraft equipment: a ULD is legally part of the aircraft, built to airworthiness standards, weighed and inspected — which is why a battered can gets pulled from service the way a cracked wheel would.

Three of these carry most of the world’s belly freight: the LD3 (AKE) on every wide-body Airbus and most Boeings, the LD2 (DPE) on the B767 family, and the PMC pallet wherever a flat load beats a can. The AKH (LD3-45) is the special case — an LD3 footprint squashed to 114 cm so it fits the shallow holds of the A320/A321 family, the only narrow-body line with containerised cargo. At the top end, the AMA (M1) is a full-height main-deck box, roughly four LD3s’ capacity in one unit.

Note how light the hardware is. An LD3 tares at ~82 kg against a 20 ft sea container’s ~2,230 kg — aluminium versus Corten steel, because every kilogram of tare is a kilogram of revenue payload burned in fuel. It is also why ULDs dent so easily, and why ground crews treat them (in theory) like aircraft parts rather than boxes.

An LD3 container measures 156 × 153 × 163 cm (61.4 × 60.2 × 64.2 in) externally, holds 4.3 m³ and is certified to 1,588 kg maximum gross at a tare of about 82 kg — the same unit the spec table above lists under its IATA code AKE. One base corner is cut away at an angle so the can nests against the lower-fuselage curve, which is what makes the LD3 a belly container rather than a simple box.

Those numbers make it the default cell of air freight planning: quotes for wide-body belly capacity are effectively quotes in LD3 positions, at roughly 1.5 tonnes and four cubic metres per position. Cargo that exceeds 163 cm of height, or a single piece heavier than the gross rating, leaves the LD3 world entirely and needs a pallet position instead.

An LD7 is the traditional name for the netted 88 × 125 in pallet load: a PAG-coded aluminium pallet with a 318 × 224 cm base, building to roughly 10 m³ under the net at a maximum gross of 6,033 kg. The name predates the IATA letter codes, so quotes may say LD7, PAG or P1P for what is physically the same lower-deck pallet position.

The PMC is its wider sibling — 96 × 125 in (318 × 244 cm), rated to 6,804 kg, about 11 m³ when built to the belly contour — and has largely displaced the 88-inch base as the workhorse pallet of the fleet. On a freighter main deck the same PMC base builds far higher than in a belly, which is where the ~17.5 m³ M1-class figures in the table come from.

Compatibility is fixed by hold cross-section, and the fleet splits cleanly. LD3-compatible lower decks: A330, A340, A350, B777, B787 and B747 all take LD3s two abreast — a B777-300ER swallows up to 44 of them, an A330-300 up to 32–33, plus bulk-hold loose cargo. The same holds accept PMC/PAG pallets and the double-width LD6 in place of LD3 pairs. The B767 exception: its narrower fuselage takes the LD2 (and its double-width sibling LD8) two abreast; an LD3 fits a 767 only solo per row, wasting a third of the hold width — which is why LD2s exist at all.

Narrow-bodies: the A320 family accepts the cut-down AKH (LD3-45); Boeing 737 holds are bulk-loaded by hand, no ULDs at all. Freighter main decks: B747F, B777F and A350F carry PMC pallets contoured to ~3 m tall and M1 containers on the main deck, with standard LD3/PMC positions below. The practical consequence for shippers: belly capacity on a passenger wide-body prices and books like a fleet of 1.5-tonne cells, while a freighter sells 6-tonne pallet positions — and cargo taller than ~160 cm cannot fly in a belly can at all.

Temperature-controlled air freight — pharmaceuticals above all — moves in powered or passive cool containers whose codes start with R. The RKN is an LD3-footprint reefer (~1 pallet position, roughly 3 m³ usable) and the RAP an LD9/PMC-footprint unit taking 4–5 euro pallet stacks. Active units (Envirotainer, va-Q-tec, CSafe are the big lessors) hold setpoints between −20 and +20 °C on battery power and compressor or dry-ice cooling, with autonomy of roughly 60–120 hours depending on model and ambient — enough for a trans-continental routing including tarmac time, which is where most cold-chain excursions actually happen.

They rent by the trip at rates that dwarf the freight itself, and they weigh: an active RKN tares around 500–600 kg against the 82 kg of a plain AKE, all of it deducted from payload. The economics only close for cargo where an excursion costs more than the container — which describes vaccines and biologics exactly.

Ocean and air capacity are quoted in units that never meet on one page, so here is the bridge. An LD3 holds 4.3 m³ — almost exactly 13% of a 20 ft sea container’s 33.2 m³. Repacking a full 20 ft box for the air leg therefore takes 7–8 LD3s in practice (the geometric 7.7 units, degraded slightly by the LD3’s angled corner and curved packing losses). A 40 ft container (67.7 m³) converts to 15–16 LD3s or about 6 PMC pallet loads; a 40 ft high cube (76.4 m³) to 17–18.

Weight tells the sharper story. The 20 ft box carries ~28,000 kg of payload; 7–8 LD3s carry at most 7×1,500 ≈ 11–12 tonnes between them. Sea freight fills volume and weight together; air freight runs out of weight allowance long before space when cargo is dense — which is why sea-to-air repacks split one container across many flights, and why the mode switch is priced per kilogram, never per box. To run your own cargo through both systems, start from its volume in the CBM calculator and the per-container capacities in the container CBM guide.

Every ULD wears a code like AKE 12345 LH: three letters, a serial number, and the owner’s airline code. The letters decode mechanically. First letter — type: A = certified aircraft container, P = certified aircraft pallet, R = thermal (reefer) container, F = non-certified pallet. Second letter — base size: K = 156 × 153 cm (the LD3/LD2 footprint), A = 318 × 224 cm (88 × 125 in), M = 318 × 244 cm (96 × 125 in), Q and others cover the rarer bases. Third letter — contour and compatibility: the shape of the shoulders and which holds accept it — the E in AKE marks the classic angled-corner lower-deck contour, the H in AKH the half-height A320 profile.

So AKE = certified container, LD3 base, belly contour; PMC = certified pallet, 96 × 125 in, contour C; RKN = reefer on the LD3 base. The system is the air-side sibling of the ISO 6346 codes on sea container doors, decoded in our ISO standards guide — same idea, different alphabet.

Both modes protect themselves against light, bulky cargo, but with different divisors. Air freight charges the greater of actual weight and volumetric weight at 1:6,000 — volume in cm³ divided by 6,000, i.e. 1 m³ = 167 kg. Sea LCL uses 1:1,000 (1 m³ = 1,000 kg), so almost all ocean cargo is billed by volume while almost all typical consumer cargo (100–150 kg/m³) is billed volumetrically by air. A 4.3 m³ LD3 filled with light goods bills as at least 718 kg of chargeable weight regardless of what the scale says.

The full mechanics — DIM factors for sea, air and courier, with worked examples — are in the CBM calculator. The one-line summary: sea sells you a box, air sells you kilograms, and the ULD is just the tray they load them on.