Air Cargo ULD Load Planning: Building Up a Unit Load Device

Quick answer: Air cargo moves in Unit Load Devices (ULDs) — contoured containers and pallets that lock into an aircraft hold. Planning a ULD build-up means fitting cargo inside a shape that isn’t a rectangle, against a weight limit that is quoted gross (including the ULD’s own tare), and a billed weight that is usually volumetric, not actual. It is a different job from aircraft weight and balance, which is the airline’s.

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Two jobs both called “load planning”

Search for air load planning software and you’ll get results for two unrelated problems. Knowing which one you have saves a lot of wasted evaluation:

	ULD build-up planning	Aircraft weight & balance
Question	What cargo goes into this ULD, and how?	Where do the loaded ULDs go in the aircraft?
Owned by	Shipper, forwarder, ground handler	Airline load control / dispatch
Governed by	ULD contour, MGW, cargo rules	Aircraft trim, CG envelope, structural limits
Output	A build-up plan for the warehouse	A load sheet and trim sheet for the flight

This guide covers the first. If you need the second — trim sheets, CG envelopes, certified load control — that’s specialised airline software and a regulated function, not a cargo-fitting tool.

Why a ULD isn’t a box

The single biggest difference from sea freight: a lower-deck ULD is cut to the curve of the fuselage. One or both long sides slope inward, so the space near the roof is far narrower than the base.

That means the usual planning shortcut — treat the unit as length × width × height and fill it — overstates capacity, sometimes badly. Cargo placed in the top corners of the bounding box doesn’t exist in a real aircraft; it’s outside the shell. A stack that computes fine on paper fouls the contour on the warehouse floor and has to be rebuilt, usually at the worst possible moment.

Practical consequences:

• Tall cargo belongs in the middle. The full internal height is only available along the centreline of a contoured unit.
• Short, dense cargo goes to the edges, under the slope.
• A pallet with a net is more forgiving than a container — you build the load to the contour and net it, rather than fitting inside a rigid shell — but the same profile limits apply, because the loaded pallet still has to clear the hold.

Any tool you use for ULD planning should model the contour as space that is removed. If it treats the unit as a plain rectangle, its numbers are optimistic in exactly the way that costs you a rebuild.

Gross weight, not payload

This trips up people who come from sea freight. Container and trailer limits are quoted as net payload — the cargo, excluding the box. ULDs are quoted as Maximum Gross Weight (MGW), which includes the ULD’s own tare.

So a unit rated at 1,588 kg MGW with a tare around 80 kg gives you roughly 1,500 kg of cargo, not 1,588. On a pallet with a net and straps, subtract the pallet, the net and any protective sheeting.

usable cargo weight  =  MGW  −  ULD tare  −  net / straps / dunnage

Tare varies by unit, by manufacturer and by condition, and it’s stamped on the ULD itself. Plan against the stamped figure, not a catalogue average.

The main units you’ll meet

Dimensions vary slightly by manufacturer and airline, and ULD type codes are not fully standardised across carriers — always confirm against the operating carrier’s own ULD sheet before you build to it.

Unit	Typical base	Typical MGW	Notes
LD-3 (AKE)	~156 × 153 cm	~1,588 kg	The workhorse lower-deck container on widebodies. Sharply contoured — one lower side is cut away.
LD-11 (ALP)	~318 × 153 cm	~3,176 kg	Full-width lower hold, full bay length. Rectangular, not contoured — no fuselage taper to plan around. Note the external shell still measures ~7.9 m³ while only ~7.2 m³ fits inside it.
LD-7 (PAG / P1P)	~224 × 318 cm (88 × 125 in)	~4,626 kg	Pallet with net, built up to a contoured profile. Milder shape limit than a rigid contoured container.
PMC (P6P)	~244 × 318 cm (96 × 125 in)	~6,804 kg	The main-deck workhorse; the widest common pallet.
PAJ igloo pallet	P1P base, ~224 × 318 cm	~4,626 kg lower deck	The P1P pallet with a rigid domed shell fitted — container-style protection on a pallet position. Rated higher on the main deck.

A note on codes, because they cause real confusion: AKH is the LD3-45, a 45-inch-high LD-3 — not the LD-7. P1P is the 88-inch pallet, so it belongs to the LD-7, not the PMC (which is P6P). Getting these crossed is a common enough error that it’s worth checking any spec sheet against a second source.

Height is normally limited to around 160–163 cm for lower-deck positions and considerably more on the main deck of a freighter — but the usable height is the contour, not the maximum.

Chargeable weight is usually volumetric

Air freight bills on the greater of actual and volumetric weight. The IATA divisor is 6,000 cm³ per kg — equivalently, 167 kg per m³:

volumetric weight (kg)  =  L(cm) × W(cm) × H(cm)  ÷  6,000

Anything lighter than 167 kg/m³ — which is most manufactured goods, and nearly all packaging — bills on volume. That inverts the optimisation: for a volumetric shipment, shaving carton dimensions saves more money than shaving weight. A 2 cm reduction across a few thousand cartons can move the chargeable weight more than removing a genuine kilogram of product.

This is the same mechanism as sea and courier dim weight, with a different divisor — see dimensional weight vs CBM chargeable weight for the full comparison.

A workable build-up sequence

1. Confirm the unit with the carrier — type, contour, MGW, and the tare stamped on that specific ULD.
2. Compute chargeable weight for the shipment and check whether you’re volume- or weight-driven.
3. Sort cargo by density and height. Dense and short to the contoured edges; tall to the centreline.
4. Build in layers you can actually stack — respect the cargo’s own stacking limit, not just the space.
5. Check the running weight against MGW minus tare as you go, not at the end.
6. Leave the profile clear. Build to the contour, not to the bounding box.
7. Net and secure, then verify the finished profile against the unit’s template.

Planning ULDs alongside your sea and road freight

Most shippers don’t do air only — the same cargo goes by sea when there’s time and by air when there isn’t, and the packing question is the same question with a different vessel.

ContainerMath includes air cargo ULD presets in the same planner as its sea containers and road trailers, so a shipment can be planned against a ULD the same way it’s planned against a 40ft. The contour is modelled as space removed from the bounding box, so a plan never promises room the fuselage curve doesn’t leave. Public dimensions for every unit are listed on the container dimensions reference.

Note that air cargo ULD planning is available on the Pro Plus and Custom plans — see pricing for the full comparison.

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Frequently asked questions

What is a ULD in air cargo?

A Unit Load Device — the container or pallet that cargo is built onto before it’s loaded into an aircraft. ULDs lock into the hold’s rail system, so cargo is handled as a few large units rather than thousands of loose pieces. Lower-deck ULDs are contoured to the fuselage curve.

What are the dimensions of an LD-3 container?

An LD-3 (code AKE) has a base of roughly 156 × 153 cm and stands about 163 cm tall, with a maximum gross weight near 1,588 kg. One lower side is cut away to follow the fuselage, so the usable shape is not a rectangle. Confirm exact figures against the operating carrier’s ULD sheet.

Is ULD maximum gross weight the same as payload?

No, and this is a common and expensive mistake. MGW includes the ULD’s own tare weight. Subtract the tare stamped on the unit — plus any net, straps and dunnage — to get the cargo weight you can actually load.

How is air freight chargeable weight calculated?

Air freight bills on the greater of actual weight and volumetric weight. Volumetric weight uses the IATA divisor of 6,000 cm³ per kg: length × width × height in centimetres, divided by 6,000. That works out to 167 kg per cubic metre.

Can I use container loading software for air cargo ULDs?

Yes, provided it models the contour rather than treating the ULD as a plain rectangle, and understands that ULD weight limits are quoted gross. A tool that fills the full bounding box will overstate capacity and produce build-ups that foul the aircraft profile.

Does ULD planning software do aircraft weight and balance?

No. Cargo-fitting tools plan what goes into a ULD. Aircraft weight and balance — deciding where loaded ULDs sit in the aircraft, and keeping the centre of gravity inside the certified envelope — is a regulated load-control function performed by the airline with its own certified systems.