The cost of mailing to Japan depends on the size and weight of the package, the value of the package, the type of mailing selected, such as First-Class or Priority Mail International Flat-Rate, and whether or not you buy the postage at the post office or online. For instance, a one pound package with no value costs $16.75 at the post office for First-Class International mailing as of 2014, while the same item packaged for Priority Express can range from $24.75 to $80.50, depending on which sized Priority Mail International box is used. Buying the postage online can save approximately 5 percent to 10 percent off the regular cost, depending on the type of mailing selected.

Obtaining Actual Cost

The best way to determine the actual cost of mailing a package to Japan is to take the package to a U.S. Postal Service facility. If it is your own packaging, the postal clerk will weigh and measure the box. If using a Flat-Rate box, you will also be asked the value of the contents because there is a maximum value of $400 that can be shipped using certain Flat-Rate options. Based on this information, the clerk can provide the exact cost to ship the package.