Air freight calculation is made as a function of the cargo gross weight, or of the weight-volume, whichever is greater.
First off, calculate cargo volume; the formula is length x width x height in centimeters. The result is divided by the factor 6,000 cm3, to obtain the “weight volume”. The latter is compared against the gross weight of the cargo to determine which is greater.
For example, if a shipment weighs 25.4 kg, and length is 70 cm, width is 35 cm, and height is 100 cm, freight calculation is as follows: 70 cm x 35 cm x 100 cm divided by 6,000 cm3, which results in a weight-volume of 40.8 kg. By comparing the weight volume (40.8 kg) against the gross weight (24.4 kg), you will see that the weight-volume is greater and, therefore, this ought to be taken to calculate the air freight. Nonetheless, you will have to round up the weight-volume to the highest half-kilo: 41 kg, which shall be multiplied by the unit air freight that is applicable to the shipment.