There is something called Cubic loading that reflects better than wing loading the lightness of any size plane in air, I don`t have the ecuation but you can think about the relationship between a fluid (air) and an object; it relates to Reynolds numbers and it depends on the fluid viscosity and the lengh of the object; it is like moving a spoon in the soup and then in the air, same ocurs with planes but the viscosity of air is constant and the diferent size of the plane can make a similar effect

Maybe someone would provide the way cubic loading can be calculated

hope this helps