We mostly ship books. For international orders USPS first class rates become more expensive than priority flat rate for some weight ranges. However since there is a limit of thickness for flat rate we can only fit so many books in a flat rate box. I found that the international first class rate can be approximated by the equation 3.5 +7.04x where x is weight in pounds My question is if it is possible to add thickness of the book as an attribute like weight so that we can decide programatically if flat rate box can be used.
Thanks
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