According to the USPS Postal Bulletin, first class rates only go to 13 ounces and are not sensitive to distance (zip codes of sender and recipient). Over 13 ounces, you go to Priority Mail up to 16 ounces, also not sensitive to distance. Over 16 ounces (one pound) the fee depends on the 'zone'. Zones 1,2, and 3 have the same rates. There are zones 4,5,6,7, and 8 which cover greater distances that the snail has to travel. You can get zone charts on the USPS web site if you want to calculate your own.