You are quoted three dollars a kilo, you ship a 50 kg consignment, and the invoice says 400 dollars rather than 150. Nothing has gone wrong. You have met chargeable weight, and it is the single most misunderstood mechanic in air freight.
The short answer
You pay on the greater of actual weight and volumetric weight. Volumetric weight is length times width times height in centimetres divided by 6,000. An aircraft is constrained by both what it can lift and the space in its hold, so light bulky cargo pays for the volume it occupies rather than the mass it contributes.
Calculating volumetric weight
The standard IATA divisor is 6,000, which treats 6,000 cubic centimetres as equivalent to one kilogram, or 167 kg per cubic metre.
Worked example. A carton measuring 60 x 50 x 40 cm:
- Volume: 60 x 50 x 40 = 120,000 cm3
- Volumetric weight: 120,000 / 6,000 = 20 kg
- Actual weight: 8 kg
- Chargeable weight: the greater, so 20 kg
You pay for 20 kg while shipping 8. The ratio is the whole game: at 167 kg per cubic metre, anything less dense than water-ish packaging pays on volume.
Two details that catch people out. Dimensions are measured to the outside of the packaging, including pallet and any overhang, not to the product. And each dimension is normally rounded up to the next whole centimetre before the calculation, so a 60.2 cm carton is measured as 61.
Express courier uses a different divisor
Integrators such as DHL, FedEx and UPS commonly apply a divisor of 5,000 on international express, which is 200 kg per cubic metre. The same carton above becomes 24 kg rather than 20. Compare an express quote with an air freight quote on chargeable weight, not on the rate per kilo, or you will compare two different things.
How the rate itself is built
Air freight is quoted per kilogram of chargeable weight, and the rate is not one number:
- Base rate. Set by airport pair, commodity and market conditions. Volatile, and it moves with capacity as much as with demand. Much of the world's air cargo travels in the belly of passenger aircraft, so passenger schedules move freight rates.
- Break points. The rate per kilo steps down at thresholds, typically +45, +100, +300, +500 and +1000 kg. This produces the most useful trick in air freight, below.
- Fuel surcharge. Per kilo, published by the airline, and often a large share of the all-in cost.
- Security surcharge. Per kilo, covering mandatory screening.
- Airport handling and terminal fees at both ends.
- Airway bill fee, per consignment.
- Dangerous goods surcharge where applicable, plus specialised handling for temperature-controlled or valuable cargo.
The break-point trick
Because the rate steps down, a shipment just below a break point can cost more than a heavier one just above it. If you have 290 kg chargeable and the +300 rate is materially lower, ask your forwarder to quote it as 300 kg. Paying for ten kilos you do not have is a discount, not a loss. Any competent forwarder does this automatically, and it is worth asking whether they did.
Cutting the bill
Since most air shipments pay on volume, packaging is the lever:
- Remove void space. Air inside a carton is the most expensive thing you will ship.
- Size cartons to the product rather than using one standard box for everything.
- Watch pallet overhang. It is measured, and it is charged.
- Reconsider pallet height. Building to the height limit of the ULD position matters more than floor area.
- Question the pallet itself. On air freight a wooden pallet adds real chargeable weight and often ISPM 15 obligations; see the wood packaging rules.
- Consolidate. Break points reward larger single consignments over several small ones.
For products where volumetric weight runs three to five times actual weight, packaging redesign is usually the largest single saving available on the lane. Export packaging and palletisation covers doing it without weakening the load.
Getting a quote you can compare
Give the forwarder piece-level dimensions and weights, not a total. Ask for the all-in cost including fuel, security, handling and airway bill fee, and ask which divisor was applied. Confirm whether the quote is airport to airport or door to door, because the road legs and customs are frequently excluded and are not small. Getting comparable quotes covers the rest.
One liability note worth knowing: carrier liability for air cargo under the Montreal Convention is capped at 26 SDR per kilogram, revised upward from 22 in December 2024, which is roughly 35 US dollars per kilo. That is a cap per kilo of actual gross weight, not a valuation of your goods, and for most cargo it is well below replacement cost. See carrier liability limits.
