Obtain shipping rates dynamically via the USPS Shipping API for your orders. Get shipping rates from the USPS API which handles both domestic and international parcels. Get real-time rates from the largest shipping network in the US Show your customers accurate shipping rates automatically with our integration for USPS, the largest delivery network in United States. Your store must use US Dollars for its currency and the United States, US Virgin Islands or Puerto Rico as the base country. It works with inches (in) and pounds (lbs), but other units can be converted automatically. USPS calculates quotes worldwide.