Calculating the cost of shipping by air depends on the “whichever is greater” principle between the actual weight and the volumetric weight. In the event that the shipment has a volumetric weight greater than the actual weight, shipping fees will be charged for the greater volumetric weight.

Transport companies use a density ratio to determine volumetric weight. This ratio depends on the type of shipment and varies from one company to another. In the example I mentioned, a density ratio of 1:5 was used.

The formula mentioned to calculate volumetric weight is: Volumetric weight = length * width * height / 5000 * number of boxes = volumetric weight in kilograms

In your example, the volumetric weight was 36kg and the actual weight was 30kg, so shipping will be charged for the higher volumetric weight, i.e. 36kg.

This shows the importance of considering dimensions and weight when shipping goods by air to avoid paying additional fees due to excess volumetric weight.