An aircraft runs out of space long before it runs out of lifting capacity when it is loaded with light, bulky cargo. To price that fairly, air freight is not billed on the weight shown on the scale alone. It is billed on chargeable weight: the greater of the shipment's actual gross weight and its volumetric weight.
The formula
Volumetric weight — also called dimensional weight — converts the space a shipment takes up into kilograms.
Volumetric weight (kg) = length × width × height (cm) ÷ 6000
The divisor of 6000 is the long-standing convention for general air cargo. It is the same as saying that one cubic metre is charged as 167 kilograms. Cargo denser than that is charged on its actual weight; cargo lighter than that is charged on its volume.
Chargeable weight is then simply the larger of the two figures, normally rounded up to the next half kilogram.
Worked examples
A dense shipment. One pallet of machine parts measures 120 × 80 × 100 cm and weighs 400 kg.
Its volume is 120 × 80 × 100 = 960,000 cm³, which gives a volumetric weight of 960,000 ÷ 6000 = 160 kg. The actual weight is higher, so the chargeable weight is 400 kg.
A light shipment. One pallet of garments measures 120 × 100 × 150 cm and weighs 200 kg.
Its volume is 120 × 100 × 150 = 1,800,000 cm³, which gives a volumetric weight of 1,800,000 ÷ 6000 = 300 kg. That is more than the actual weight, so the chargeable weight is 300 kg — the airline bills 100 kg more than the scale shows.
Several pieces. For a consignment of several pieces, the volumetric weight is worked out on the total volume of the consignment and compared with its total actual weight. Ten cartons of 60 × 40 × 40 cm weighing 12 kg each have a volume of 960,000 cm³, a volumetric weight of 160 kg and an actual weight of 120 kg, so the chargeable weight is 160 kg.
Measure the way the airline will
The dimensions that count are the outermost ones, including the pallet, any overhang, and bulges in the wrapping. An irregular piece is measured as the rectangular box that would contain it. Three points regularly catch shippers out:
- A carton that overhangs the pallet by five centimetres on each side is measured at the wider figure.
- The pallet itself adds roughly fifteen centimetres of height and its own weight.
- Cargo that cannot be stacked may be charged for the space above it, because nothing else can be loaded there.
Handling agents re-measure cargo on acceptance, and the airline bills on its own figures. A booking made on optimistic dimensions produces an invoice that does not match the quote.
Why the divisor matters
Not every service uses 6000. Express integrators and courier products commonly use 5000, which turns the same carton into a heavier chargeable weight — the 300 kg garment pallet above becomes 360 kg. Road freight and LCL ocean freight use different conversions again; in LCL, one cubic metre is treated as one tonne.
When comparing quotes, check the divisor before comparing the rate per kilogram. A lower rate on a 5000 divisor can cost more than a higher rate on 6000.
Rate breaks and the minimum
Air freight tariffs are stepped by weight: a minimum charge, then a normal rate for small shipments, then lower rates per kilogram at breakpoints such as 45, 100, 300, 500 and 1000 kg. Because the rate drops at each break, a shipment just under a breakpoint can be cheaper when declared at the breakpoint. A 290 kg shipment may cost less billed as 300 kg at the lower rate. Forwarders check this as a matter of routine.
Remember too that the freight rate is only part of the bill. Fuel and security surcharges are normally charged per kilogram of chargeable weight as well, so every volumetric kilogram is paid for more than once.
Reducing chargeable weight
The cheapest kilogram is the one that is not volumetric. Practical steps:
- Right-size the cartons. Void fill is charged as if it were cargo. Cutting ten centimetres off the height of a carton cuts its volumetric weight in proportion.
- Pack to the pallet footprint. Avoid overhang; it adds chargeable volume and invites damage.
- Mix dense and light cargo. Because the calculation is done on the whole consignment, heavy pieces offset bulky ones when they move on the same air waybill.
- Check stackability. Mark and pack cargo so that it can be stacked where the goods allow it.
- Compare modes. Very light, bulky freight that is not urgent may suit sea or road better. Where both are options, compare the door-to-door cost against the days saved.
Get the dimensions right at the quotation stage, and the chargeable weight on the invoice should hold no surprises.
