I'm working my way through the listing process. Did one so far, but am not sure I did it right. I ship by Priority mail but all of my items will be varied sizes and weights. When I do a listing the only options I see are Weight and Package size (normal or large etc). I am accustomed to listing both weight and box size like 12"x!2"x!2" or 18"x12"x12". I do not know if the calculator will return an accurate price just using box girth. Is there a way to enter a specific box size on each listing? Thanks for the help!