Thanks in advance people :)
I don't think it is a real amount. There is additional fuel weight (which is pretty close to zero) Many planes have weight restrictions, so if too many bags are heavy, either people or bags have to be taken off (which costs the airline money) There is also in increased chance of injury from lifting larger bags. Also more worker time and energy is spent on larger bags. I think the number is one that will discourage most people from over-packing but will not break the bank of someone who is over-packed. If everyone could bring how much they want, most planes would be cargo planes more than passenger planes.
about US$0.15 per kg,now that pricings are higher.....
the cost for luggage per kg is based on the market rate not the cost to the airline. if they charge too much, no one will take excess luggage. if they charge too little everyone will ship excess luggage. so they have over the years used a trial and error method to come up with an industry standard. This is not based on actual cost so there is no way to give you a figure.