Decibel.
The word "volume" represents the relative "loudness" of a sound. The word "decibel" is a unit of measurement for sound.
Loudness.
· unit
you can use the word loudness
loudness
Joule is a unit of energy.
ugly, unit, upon
The sone was proposed by Stanley Smith Stevens as a unit of perceived loudness in 1936. Loudness is the subjective perception of sound pressure. According to Stevens' definition, the sone is equivalent to 40 phons, which is defined as the loudness level of a 1 kHz tone at 40 dBSPL. The number of sones to a phon was chosen so that a doubling of the number of sones sounds to the human ear like a doubling of the loudness.
Loudness.
Sound pressure goes e.g. through thin paper. Loudness is a problematic word in this case. Feelings are different from person to person. So don't talk of "measuring" the "loudness". You can really measure the sound pressure (amplitude) with a sound pressure level meter. Microphones and eardrums are only sensitive to the sound pressure.
unit is what you measure by for example: cm, ft, in, mm, m, yd, etc.
A Joule … the standard unit of measure of Energy. (or an Erg which is equal to Joule^-7)