1-3 Address Placement for Letters 1-3.1 Nonmailable Placement of the Delivery Address The placement of the delivery address on a letter-size mailpiece may make a piece nonmailable or nonmachinable. A letter-size mailpiece is nonmailable if any of the following circumstances apply: The length (the dimension parallel to the delivery address) is less than 5". Example: For a letter-size piece that is 4" by 6" (which indicates that the delivery address is parallel to the 4" dimension, which means that its length is 4"), its 4" length is less than the minimum required length of 5". This piece is nonmailable. The height (the dimension perpendicular to the length) is less than 3 1/2". Example: For a mailpiece (including a letter-size mailpiece) that is 6" by 3" (which indicates that the delivery address is parallel to the 6" dimension, which means that its length is 6" and its height is 3"), its 3" height is less than the minimum required height of 3 1/2". This piece is nonmailable. The aspect ratio (length divided by height) is not between 1.3 and 2.5, inclusive. Example: For a letter-size piece that is 5" by 8" (which indicates that the delivery address is parallel to the 5" dimension, which means that its length is 5" and its height is 8"), its aspect ratio (5" length divided by 8" height) is 0.625, which is not between 1.3 and 2.5, so it is mailable but as a nonmachinable letter.