Air freight is billed on chargeable weight, not actual weight, and chargeable weight is whichever number is higher between what the shipment actually weighs and what it would weigh if it were as dense as the airline’s benchmark. Light, bulky cargo gets charged on volume, not scale weight.
Why volumetric weight exists
An air cabin has a fixed amount of space, not a fixed amount of weight capacity, for most general cargo. A shipment of pillows and a shipment of steel brackets can weigh the same on a scale but take up wildly different amounts of cargo hold space. Volumetric weight translates space into an equivalent weight figure so airlines can price for the resource that’s actually scarce, space, not just mass.
The divisor that trips people up
IATA’s standard air freight divisor is 6000 cm³ per kg (or 166 in³ per lb). Ground and ocean freight use completely different divisors, which is why a shipment’s “dimensional weight” looks different depending on which mode you’re pricing it for. Some air carriers and some regions use a 5000 divisor instead, always confirm which one your quote is actually using, since it changes the chargeable weight meaningfully.
Fuel and security fees aren’t optional line items
Nearly every air waybill carries a fuel surcharge and a security fee on top of the base rate, both calculated as a percentage of the freight charge. A quote that only shows the per-kg base rate without these isn’t the number you’ll actually be billed, always ask for the all-in rate or add these yourself before comparing quotes.
Check US import duty and fees next if this shipment is also clearing customs into the US.