An airline sells space, not mass. A shipment that weighs little and fills a lot would travel almost free if it were billed on the scale, so the industry converts volume into a weight and charges whichever number is higher. The conversion is a division: cubic metres divided by a divisor, which for IATA general cargo is 6000 — the legacy of 6000 cubic centimetres per kilo. One cubic metre therefore becomes 166.7 kg.
The number the carrier bills is the higher of the two, rounded up. IATA rounds to the next half kilo, and it rounds up even by a gram — 128.02 kg is billed as 128.5 kg. Rounding to the nearest instead of upward is the commonest quiet error in a manual quote, and it always loses money in the same direction.
The row worth reading is density. Below 166.7 kg per cubic metre the volume is winning and you are selling space; above it the scale is winning and you are selling mass. A forwarder who can say "your cargo runs at 62 kilos per cube, so the aircraft charges for the room" has ended the argument before it starts.
Because the cargo is taking more space than its mass justifies. Divide the volume in cubic metres by the divisor — 6000 for IATA air — and if that number is bigger than the scale reading, that is what you pay for. It is not a surcharge and it is not negotiable at the airport; it is how the space is sold.
IATA general air cargo is 6000 cubic centimetres per kilo, which is 166.7 kg per cubic metre. The integrators — DHL, FedEx, UPS — use 5000, which is 200 kg per cubic metre and therefore about 20% more expensive on light cargo. European road freight conventionally uses 3000. Always check the tariff in front of you; the divisor is a commercial term and it can be negotiated on volume.
Up, to the next 0.5 kg, under IATA rules — never to the nearest. 40.1 kg is 40.5 kg and 40.6 kg is 41.0 kg. Below 1 kg most tariffs still bill a full kilo, and almost every lane has a minimum charge that overrides the weight entirely on small shipments.
At the pivot, which is 1000 divided by the divisor expressed per cubic metre: 166.7 kg/cbm on a 6000 divisor, 200 kg/cbm on 5000, 333.3 kg/cbm on 3000. Lighter than the pivot and you are billed on space; heavier and you are billed on the scale. Garments, foam, empty packaging and most e-commerce cartons sit well below it.
No. Ocean LCL uses the revenue ton — the higher of one cubic metre or one metric tonne — rather than a divisor, so the pivot sits at 1000 kg per cubic metre instead of 166.7. Cargo that is heavily volumetric by air can be perfectly ordinary by sea.
Cargo-Stack reads the enquiry, prices it against your own rates, and drafts the quote — with this arithmetic underneath it. Same maths, no retyping.
Try it on a real enquiry