Mine is hard to determine nowadays as the loudness is variable, it is mild but it gets all the way to moderate when it spikes and that happens pretty often (several times a day), when it's moderate I can hear it over most background noises, especially as it's 14kHz high pitched. When it's mild, I seldom hear it. More often than not, it's at moderate level however.
When it initially started however, it was severe for 23 days, with a stable SL of roughly 60 to 65 dB (closed to 65), and was extremely debilitating. Then on the 23rd day, it just went to mild, it stayed that way until I stopped prednisone, then it went to moderate, I still rather not take prednisone than having it go back to mild, the side effects for this drug can be pretty nasty.
Loudness is only part of the issue however, how someone reacts to the noise may have a much more significant impact to how significant of an impairment the tinnitus brings. That said anything louder than 30 dB is what I would consider severe tinnitus, when taking into account SL alone as that would likely have a significant impact on your ability to focus.
Tinnitus has however more to do with how much distress it brings and how debilitating it is, than how loud it actually is.