8 watts to 80 watts is 10 dB?Yes, it is.
The ratio of two power levels, expressed in db and with the two levels denoted as P1 and P2, is 10log(P1/P2), where "log" is the base-10 logarithm.
It doesn’t matter whether the higher or the smaller number is placed in the numerator (P1) or the denominator (P2). The magnitude of the answer will be the same either way, with a sign that is positive if P1 is larger than P2, and negative if P1 is smaller than P2.
10log(80/8) = 10 db
10 log(8/80) = -10 db
Elevick is also correct that a 10 db increase in volume will be subjectively perceived as "twice as loud." As a good approximation, at least.
Regards,
-- Al