priority mail flat rate international prices are shipping costs offered by USPS for sending packages internationally using flat rate boxes. These prices are the same regardless of the weight (as long as the package fits in the designated box size) or destination country, providing customers with a straightforward and predictable shipping cost for international deliveries. USPS offers various sizes of flat-rate boxes for international shipping, making it easier for customers to choose the right option based on their needs while avoiding fluctuating shipping costs.