Ok-- I have a 1/2" thick document (41 pages) from the post office with all the new rates. Hope this information helps
A regular one ounce first class stamp will cost $.44 Domestic Flat Rate:
$10.35 - Small Flatrate - up to 70 lbs.
$13.95 - Large Flatrate - up to 70 lbs. I didn't include all of the various weights only the maximum First Class rate for Canada and Mexico
$16.77 - International First Class to Canada - 4 lbs.
$26.85 - International First Class to Mexico - 4 lbs. International Flat Rate to both Canada and Mexico with a maximum weight of 20 lbs:
$25.95 - Small Flat
$32.95 - Large Flat
I don't have the deminsions of the flat rate boxes, but you use the same boxes for dometic and international - it's just the maximum weight is different. From experience, the large flat rate boxes are not much larger than the small ones.