shipping one purchase in 2 boxes

[5spareroom3]

I'm looking into selling a large lot of books. Because of the weight, I'd like to break this down into shipping 2 boxes, will I have a problem with figuring the weight and box dimensions to be accurate when I fill out my sale description and shipping options?

[partial*eclipse · Accepted solution]

Pack the boxes, weigh them, look up the postage cost for Media Mail, add the two prices together, and use this as a flat shipping cost for your listing.  

If you run up against the maximum allowed flat price for shipping in your category, then you'll have to use the Advance listing form and set up calculated shipping for one box and use the postage for the other box as your handling fee.

The box dimensions really don't matter, as long as the length-plus-girth of each box  is not over 108 inches.