is flat rate shipping the cheapest depends on the size, weight, and destination of the package. is flat rate shipping the cheapest often works out to be the best option for heavier items that fit in USPS flat-rate boxes. This pricing structure allows for one fixed price regardless of weight, as long as the item fits within the designated box size. For lighter, smaller packages, standard shipping methods may be cheaper, so it’s best to compare shipping options based on your specific needs.