Mail delivery times vary due to factors such as package size, package type and travel time. For a standard letter in the United States, the average delivery time to another state is two to seven days, while a letter remaining in-state should arrive in one to two days.
While the United States Postal Service does provide a standard estimation, the time that mail is in transit varies based on the type of mail (letter, package, etc.), size, the distance of travel or the time of year. For an extra charge, faster, guaranteed shipping is available. When sending mail at the standard rate, however, the sender should leave at least a week for delivery.