What's the difference between First Class and Standard?

USPS only includes the time a package stays in transit in their estimations. According to USPS: Standard Mail is processed by the USPS on a “time available” basis. There is NO guaranteed delivery time, only “typicals”. Local mail is typically delivered in about two weeks. Sometimes it’s faster… but sometimes it’s slower. First Class mail is processed by the USPS on a priority basis; it goes to the front of the USPS line. Typically delivered in 1-4 days