Dimensional Standards for Letters
Letter-size mail is:
a. Not less than 5 inches long, 3-1/2 inches high, and 0.007-inch thick.
b. Not more than 11-1/2 inches long, or more than 6-1/8 inches high, or more than 1/4-inch thick.
c. Not more than 3.5 ounces.
d. 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 0.125 inch (1/8 inch).
.2 Nonmachinable Criteria
A letter-size piece is nonmachinable (see 6.4) if it has one or more of the following characteristics (see 601.1.4 to determine the length, height, top, and bottom of a mailpiece):
a. Has an aspect ratio (length divided by height) of less than 1.3 or more than 2.5.b. Is polybagged, polywrapped, or enclosed in any plastic material.
c. Has clasps, strings, buttons, or similar closure devices.
d. Contains items such as pens, pencils, or loose keys or coins that cause the thickness of the mailpiece to be uneven (see 601.11.18, Odd-Shaped Items in Paper Envelopes).
e. Is too rigid (does not bend easily when subjected to a transport belt tension of 40 pounds around an 11-inch diameter turn).
f. For pieces more than 4-1/4 inches high or 6 inches long, the thickness is less than 0.009 inch.
g. Has a delivery address parallel to the shorter dimension of the mailpiece.
h. Is a self-mailer with a folded edge perpendicular to the address if the piece is not folded and secured according to 201.3.13.1.
i. Booklet-type pieces with the bound edge (spine) along the shorter dimension of the piece or at the top, unless prepared according to 201.3.13.
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