a) Normally the billable weight is depending on the actual weight and the volumetric weight, For instance. The dimension for single package is 50x40x50cm but the gross weight is 10kgs only, the way of calculating the chargeable weight is 50x40x50cm/5000=20kgs (Formula is Length x Width x Height in centimeters divide 5000). So the final billable weight is 20kgs instead of 10kgs. We’ll remeasure size and reweigh the packages once the goods arrived at Top shipping’s warehouses. Our target is make sure all of the info is correct before issuing invoice to you. b) the formula of calculating the air cargo is Length x Width x Height in centimeters divide 6000.