B/A Ratio is the "Boob to Arm" ratio which signifies the relation between the circumference of a girl's arm to the size of her chest and breasts. A large B/A ratio is considered highly attractive (i.e. large breasts / small arms), an equal ratio, neutral (small breasts/ small arms or large breasts/ large arms) and a low ratio, unattractive (large arms, small breasts)..
by dustin SB March 11, 2008