For me, very loud ! It is a subjective thing, however when I use my 32 Ohm headphones (over the ear isolating DJ headphones) I have to reduce the gain by -18 dB (eight times reduced levels) to make it approach a comfortable listening level. I find anything above that very loud.
If you were to use 16 Ohm headphones, then it would be a reduction of sixteen times to make it comfortable !
NOTE : there is enough power out of the headphone socket to damage your hearing. Please look after your hearing and if you listen to music loud when using headphones, do it for very short durations, such as one song only.