postal service weight rates are the fees charged by postal services based on the weight and size of a package being mailed. Different postal services, like USPS, UPS, and FedEx, use weight-based pricing to determine the cost of shipping, with heavier packages typically incurring higher fees. For USPS, weight rates are applied to services like Priority Mail and First-Class Package, where the cost increases based on the weight of the package. To save on shipping costs, it’s important to accurately measure the weight and dimensions of the item being shipped and consider using flat-rate shipping options if the package is heavy.