The U.S. Postal Service calculates the cost of shipping for a package based on the package's size, weight and destination, as well as the specific mailing service the sender selects. To help senders estimate rates, a postage price calculator is available on the USPS website.
To calculate the price of sending a package, go to the USPS.com main page, slide the mouse arrow over Quick Tools or Mail & Ship on the toolbar at the top of the page, and click on Calculate a Price. Select the country destination of the package, and if you are sending the package within the United States, type in the zip codes of origin and destination. Enter the mailing time and date, and if there are any extraordinary materials in the package, then check the appropriate boxes. Select a flat-rate service for items under 70 pounds shipped in USPS boxes, or select the package shape as package or large package. Enter the weight of the package in standard pounds and ounces or metric kilograms, then click Continue.
The calculator then lists postal service options, expected delivery dates and prices based on the package information entered. Select the mailing service you prefer according to package contents, price, speed of delivery and extra services. Media mail is the slowest and least expensive option, but is only available for books, manuscripts, sound recordings and educational materials. Other options are standard mail, priority mail and priority mail express.