What is loudness of a sound?

Loudness of a sound is the characteristic of a sound which depend on the intensity of  energy it carries.
Intensity of a sound is the amount of energy passing through a surface area of one square metre held perpendicular per sec.
Intensity depends on square of amplitude of the wave passing. Hence we can say Loudness is directly proportional to the square of Amplitude. If amplitude is doubled, loudness becomes four times.
Loudness depends on distance of source from the listener.
Loudness depends on resonance also.