Air cargo is sold by weight, but aircraft run out of space as often as they run out of lift. That is why airlines bill on chargeable weight, the greater of actual gross weight and volumetric weight. Understanding the calculation lets shippers design packaging and consolidation that reduce cost without compromising the cargo.
The volumetric formula
Most airlines and forwarders apply the IATA standard volumetric conversion:
Volumetric weight (kg) = length × width × height (cm) ÷ 6,000
This equates to a density threshold of about 167 kg per cubic metre (1 m³ = 1,000,000 cm³ ÷ 6,000). Cargo lighter than that is billed on volume; denser cargo is billed on actual weight. Express integrators often use a lower divisor, commonly 5,000, which makes light cargo relatively more expensive.
Worked example: 5 cartons of 60 × 40 × 40 cm weighing 12 kg each.
- Volume per carton: 96,000 cm³, so volumetric weight 16 kg each, 80 kg in total
- Actual weight: 60 kg in total
- Chargeable weight: 80 kg, billed on volume
Our chargeable weight calculator runs this for any shipment. Dimensions are measured at the outermost points, including pallet overhang, and airlines round them up according to their rules.
Why density drives price
Airlines optimise each flight for both weight and volume. A flight filled with light, bulky cargo wastes lift; one filled only with dense cargo wastes space. Pricing on chargeable weight balances the two. For shippers, the levers are:
- Reduce empty space in packaging. Right-sized cartons and removing voids often lower chargeable weight more than any rate negotiation.
- Palletise with care. Pallets add height and overhang; a pallet that forces an extra layer of air in the ULD can cost more than it saves in handling.
- Consolidate. Forwarders mix dense and light cargo in the same unit load device (ULD) to use aircraft capacity efficiently, which is why consolidation rates are usually below direct airline rates.
Unit load devices
Airlines move most cargo in ULDs, standardised containers and pallets locked into the aircraft's floor system. Common types include:
| ULD | Description | Typical use |
|---|---|---|
| AKE (LD3) | Lower-deck container, contoured to fit the widebody fuselage | Loose cartons and baggage on widebody aircraft |
| PMC | 96 × 125 inch pallet with net | General cargo, contoured to main or lower deck profile |
| PAG | 88 × 125 inch pallet | General cargo |
Contour and height limits vary by aircraft type. On freighters, main-deck positions accept taller loads than passenger aircraft bellies, which matters for machinery and oversized cargo. IATA's cargo programmes publish ULD and handling standards used across the industry.
Dangerous goods and security
Many everyday products are regulated as dangerous goods in air transport, including lithium batteries, aerosols, perfumes, paints and some chemicals. Carriage is governed by the ICAO Technical Instructions, implemented in practice through the IATA Dangerous Goods Regulations (DGR). Shippers must classify, pack, mark, label and declare such goods correctly; undeclared dangerous goods are a serious safety and legal issue.
Air cargo is also subject to security controls under ICAO Annex 17 and national programmes, such as known consignor or regulated agent schemes. Cargo from a secure supply chain can be accepted without further screening; other cargo is screened before loading, which can add time.
When air makes sense
Air freight typically costs many times more per kilogram than ocean, but moves in days rather than weeks. It is usually justified for:
- High-value, low-density goods where inventory carrying cost is significant
- Perishables, pharmaceuticals and time-critical spare parts
- Launches, samples and recovery of delayed supply
Sea-air combinations, such as ocean to a Gulf hub and air onwards, can sit between the two on cost and time. Emissions differ by an order of magnitude too; see our guide to measuring freight emissions.
Frequently asked questions
How is air freight chargeable weight calculated?
It is the greater of the actual gross weight and the volumetric weight, where volumetric weight is length × width × height in centimetres divided by 6,000 under the common IATA standard.
What does the 6,000 divisor mean?
It means cargo is billed on volume when its density is below about 167 kg per cubic metre. Express couriers often use 5,000, which corresponds to 200 kg per cubic metre.
Are lithium batteries allowed in air cargo?
Yes, but they are regulated as dangerous goods. They must be prepared, packed, marked and declared according to the ICAO Technical Instructions and the IATA Dangerous Goods Regulations, and some configurations are restricted to cargo aircraft.
References
- International Air Transport Association, Cargo programmes and standards.
- IATA, Dangerous Goods Regulations (DGR).
- ICAO, Dangerous Goods and the Technical Instructions for the Safe Transport of Dangerous Goods by Air.
Prepared by the Apex Ocean Lines industry experts and editorial team, checked against the sources cited. Short forms link to our shipping glossary.