Hi Grani L, This may not be the info you were looking for but this is what I do. I don't have a large volume of shipping but, I have an account w/ usps too. I weigh with my candle scale or if it's heavier I just use my "people scale". Usps just asks you the weight so I have found that you don't have to be exact. You enter addresses "from" and "to" then the weight and it will give you options with prices. You can then choose the one u want and print and pay for the postage all from your computer. U can have the mailman pick it up from your house (or wherever) you are shipping from. It is SO convenient. HTH, Fran