All international carriers base their shipping rates on the calculated Chargeable Weight. Chargeable weight is the greater of the Actual Weight or Volumetric Weight.
Actual weight is the weight of the package when put on a scale. Dimensional Weight (volumetric weight) is calculated on the package size. Large items with a small Actual Weight, like pillows and lampshades, will very often be charged according to their volumetric weight.
Volumetric weight is calculated using the following formulas:
Length (cm) x Width (cm) x Height (cm) / 5000.
E.g. 35cm x 24cm x 29cm / 5000 = 4.87Kg.
Length (in) x Width (in) x Height (in) / 139
E.g. 21in x 17in x 14in / 139 = 35.96lbs