First-Class Mail International™ Letter
 


Dimension Minimum Maximum
Length 5-1/2 inches 11-1/2 inches
Height 3-1/2 inches 6-1/8 inches
Thickness 0.007 inch 1/4 inch


First-Class Mail International Letters


Any item smaller than the minimum dimension is not mailable.
For larger items, see Large Envelope or Package.
For envelopes, length is the dimension parallel to the address.

Letters that meet one or more of the nonmachinable characteristics below are subject to the nonmachinable surcharge. For items over 3.5 ounces, see Large Envelope or Package.

  • It is a square letter
  • It is too rigid - does not bend easily
  • It has clasps, string, buttons, or similar closure devices
  • It has an address parallel to the shorter dimension of the letter
  • It contains items such as pens that cause the surface to be uneven
  • The length divided by height is less than 1.3 or more than 2.5

    • Square Envelope
    The minimum size for a square envelope is 5-1/2 x 5-1/2 inches.
    Square letters are subject to the nonmachinable surcharge.