Many international postage services, including the United States Postal Service, have online calculators that can be used to determine necessary postage. Users must input data including package size and weight to get accurate results.
One drawback of online postal calculators is they require access to postage scales. People who do not own postage scales may choose to go to self-service postage centers that include a scale for packages and a method of printing the required stamps. Individuals can also go to the staffed counters in any post office to inquire about the number of stamps needed to send a package.