As airline regulation, the volume weight calculate method :
              L*W*H/6000(by cm), 
      want to compare the actual weight.


   for example:  50cm*60cm*50cm/6000=25kg, actual weight: 20KG, charge as; 25KG
                 
                 50cm*60cm*50cm/6000=25kg, actual weight: 30kg, charge as: 30KG
 
 if have many boxes: 
              actual weight        volume weight
   box 1:         15kg            40*50*60cm/6000=20kg
   box 2:         10kg            30*40*40cm/6000=8kg

 total acutal weight:15kg+10kg=25KG

 total volume weight:20kg+8kg=28KG

 will charge as: 28KG
  
when measure the size of box, the airline will measure the min-width of box