postal rate first class is a commonly used method for sending letters and packages within the United States. USPS First-Class Mail provides fast and affordable delivery for items such as postcards, letters, and small packages weighing up to 13 ounces. First-Class Mail is typically delivered in 1-3 business days, depending on the destination. The cost of First-Class Mail depends on the weight and size of the item, with standard rates for letters and variable rates for packages. This service includes tracking for certain mail categories and is popular among e-commerce sellers for lightweight shipments.