is first class the same as priority mail First-Class Mail and Priority Mail are both services offered by USPS, but they differ in terms of speed, cost, and package size limits. First-Class Mail is typically used for lightweight items like letters and small parcels, with delivery in 1-3 business days. Priority Mail, on the other hand, is faster and used for heavier packages, with delivery typically in 1-3 business days as well. Priority Mail includes additional services like free insurance and tracking, while First-Class Mail offers a more affordable option for smaller packages.