The aspect ratio is the length of the mailpiece divided by the height. For a letter-size piece to be machinable, this number must be between 1.3 and 2.5, inclusive. This ensures that the mailpiece travels properly on USPS machinery. Pieces that are too tall relative to their length tend to tumble during processing. See Exhibit 1-2.3.
Exhibit 1-2.3
Examples of Aspect Ratio (Not Drawn to Scale)
