In the fashion industry, a BBW is size 14 and above, and a SSBBW is size 28W and above. You really can't divide by weight when someone could be 4'8" or 6' 2"
There's all kinds of scenarios. What if people are larger than 14 on the top or bottom and smaller on the other? What about busty thin women who need a large top? What about women who are truly "big boned." There will never be a definitive answer.
