One rule, four conventions
Every mode applies the same idea — you pay for space or weight, whichever is greater — and each uses a different constant to convert space into weight.
- Air freight (IATA): volume in cubic centimetres divided by 6,000 gives kilograms. Equivalent to 166 cubic inches per pound.
- Express courier: divided by 5,000, which is 139 cubic inches per pound. Harsher on bulky freight, deliberately.
- Ocean LCL: rated per revenue ton, the greater of cubic metres and metric tons, at a ratio of 1 CBM to 1,000 kg. Quoted as W/M on the rate sheet.
- US domestic parcel: cubic inches divided by 139 gives pounds.
Reading an LCL quote
An ocean LCL rate quoted as "$48 W/M" means forty-eight dollars per revenue ton, and the revenue ton is whichever is larger: your cubic metres or your metric tons. Three cubic metres of goods weighing 1.2 tonnes rates on 3 — you pay $144. The same three cubic metres weighing 4 tonnes rates on 4 and costs $192. Freight forwarders quote this way precisely because they do not know in advance which side of your cargo will govern.
Rounding conventions
Air freight typically rounds up to the next half kilogram, express to the next whole kilogram or pound, and LCL to two or three decimals on the revenue ton. The figures above round air and express up to the next half unit and leave ocean unrounded — verify against your carrier's tariff before quoting a customer.