Postcards that exceed the normal postcard dimensions but meet the letter-size dimensions are mailable, but they incur the regular First-Class Mail letter price. See Exhibit 6-2 for dimensions for postcards.
Barcoded pieces measuring more than 6" long or 4-1/4" high must be at least 0.009" thick.
Additional standards apply to QBRM pieces.
Exhibit 6-2
Dimensions for Postcards
Letter-size Prices
Card Prices
Minimum
Maximum
Length
5"
11-1/2"
6"
Height
3-1/2"
6-1/8"
4-1/4"
Thickness
0.007"
0.016"
