ULD (Unit Load Device)

If you’ve ever shipped goods by air freight, your cargo didn’t just get tossed loose into the belly of a 747. It was loaded into a standardized container or strapped onto a contoured metal pallet designed to fit the curved interior of an aircraft fuselage. That container or pallet is a Unit Load Device, and it’s the basic building block of how air cargo moves globally.

Types of ULDs

ULDs come in two basic forms: containers (also called igloos due to their rounded shape) and pallets with netting. Containers are rigid, enclosed boxes with at least one open side for loading. They’re shaped to match specific positions in an aircraft’s cargo hold, which is why many have one angled or curved side. Pallets are flat aluminum sheets onto which cargo is stacked, then secured with netting and straps.

Each ULD type has an IATA designation code. The most common ones you’ll encounter:

• LD3 (AKE): The workhorse of lower-deck air cargo. Fits in wide-body aircraft like the Boeing 777 or Airbus A330. Holds roughly 150 cubic feet and up to 3,500 lbs. A 777F (freighter) can carry around 32 LD3 positions on its lower deck.
• LD7 (AMA): Roughly twice the size of an LD3. Commonly used on 747 freighters. Capacity of about 300 cubic feet and 13,300 lbs maximum.
• PMC (P6P): A 96″ x 125″ pallet, one of the most standard sizes in air freight. Used on the main deck of freighter aircraft and can hold up to 11,000+ lbs depending on the aircraft type.
• LD1, LD2, LD6, LD8, LD11: Various sizes for different aircraft types and cargo hold positions.

Why ULDs Matter for Air Freight Costs

Air freight is priced in two primary ways: per kilogram (for loose or consolidated cargo) or per ULD position (for larger shipments). When you’re shipping enough volume to fill or nearly fill a ULD, your forwarder may offer a “pivot weight” rate. This means you pay a flat rate for the ULD up to a certain weight threshold (the pivot), and only pay per-kilo charges above that threshold. For example, an LD3 might have a pivot weight of 1,000 kg at a rate of $4,500. If your shipment weighs 800 kg, you still pay $4,500. If it weighs 1,200 kg, you pay $4,500 plus a per-kilo rate on the extra 200 kg.

This pricing structure rewards shippers who can fill ULDs efficiently. Partial fills mean wasted space you’re paying for. That’s why consolidation matters. Freight forwarders combine multiple shippers’ cargo into single ULDs to maximize utilization and split costs.

Loading and Build-Up

ULD loading (called “build-up”) happens at cargo terminals or warehouse facilities near the airport. Goods are carefully stacked inside the container or onto the pallet to maximize space while keeping weight distribution balanced. Improper loading can cause weight-and-balance issues for the aircraft, which is a safety concern, not just an efficiency problem. Airlines and ground handlers follow strict build-up procedures, and overweight or improperly loaded ULDs get rejected.

For temperature-sensitive goods, there are thermal ULDs with insulated walls, cooling systems, or dry ice compartments. Pharmaceutical companies and fresh food importers use these extensively. For hazardous materials, specific ULD configurations and labeling requirements apply.

What Ecommerce Sellers Should Know

Most ecommerce sellers won’t book a full ULD on their own. That’s enterprise-level shipping. But understanding ULDs helps you make sense of your air freight quotes. When your forwarder quotes a “per-kg consolidation rate,” your goods are going into a shared ULD with other shippers’ cargo. When they offer a “ULD rate” or “pivot rate,” they’re suggesting your volume justifies a dedicated unit.

For high-value or time-sensitive Amazon inventory, air freight can make sense during stockout emergencies or product launches. A 3PL with freight forwarding relationships can help you decide whether consolidation or a dedicated ULD is more cost-effective, and they’ll handle the receiving and FBA prep once the cargo lands stateside. That coordination between air freight arrival and Amazon-ready prep is where days get saved or lost.