Not sure if your problem is your tinnitus or your inability to calculate it's loudness. If it's the former invest in a fan and leave it on near you when you go to sleep.

Ah, good point. I would not have the problem of inability to calculate tinnitus' loudness if I had no tinnitus in the first place, but let's say that now -- after ~3 years since its appearance -- I resigned to idea of suffering from tinnitus, so it's some how not a problem anymore, I now don't even need a fan or any other noise source to fall asleep.