Grades are as follows.
1)Silent killer = speaks for itself.
2) A fluff = barely audible wind noise.
3)A pip = what it sounds like!
4) A Trump = beats a pip every time.
5) A fart = the average type..with noise.
6) A Blower = bit louder and slightly longer than a fart
7) A ripper = sounds like tearing material.
8) A Blaster = another that speaks for itself.
9) A duckfart = comes our slowly and noisily as you walk...sounds like a quacking duck. (Best coming down stairs)
10) Killer = Also speaks for itself.
None of them have much actual weight but some obviously 'carry more weight' than others.