1-2 Physical Standards for Letters

1-2.1 Dimensional Standards for Letters

The Postal Service defines letter-size mail as follows:

1. Not less than 5" long, 3-1/2" high, or 0.007" thick. See Exhibit 1-2.1.
2. Not more than 11-1/2" long, 6-1/8" high, or 1/4" thick.
3. Rectangular, with four square corners and parallel opposite sides. Letter-size, card-type mailpieces made of cardstock may have finished corners that do not exceed a radius of 1/8".
4. Having the following maximum weights:
1. Retail Letters: 3.5 ounces. First-Class Mail letter-size pieces over 3.5 ounces are charged at the large envelope (flat) prices.
2. Machinable and Automation Letters and Cards:
1. Automation enveloped letters and cards: 3.5 ounces.
2. Machinable enveloped letters and cards: 3.5 ounces.
3. Booklets and folded self-mailers: 3 ounces.

Exhibit 1-2.1 

Minimum Letter Dimensions, Mailpieces 1/4" Thick or Less