FLATS
SHAPE &
DIMENSIONS
There is no aspect ratio for flats.
Must be rectangular (for flats, a
square is considered rectangular).
The length of a flat is the longest
dimension.
STRUCTURAL REQUIREMENTS
Must meet flexibility standards (droop test).
Must have uniform thickness that does not cause more
than 1/4” variance.
WEIGHT LIMITS
The maximum weight for a First-Class
flat is 13 oz and for a Marketing Mail
flat is 16 oz.
ELIGIBILITY
Pieces not eligible as a flat are parcels.
PROMOTIONS
May qualify for the Continuous Contact Promotion: The
Continuous Contact Promotion encourages marketing
campaigns with multiple touchpoints to adopt a more
targeted approach that drives customer behavior.
Minimum
Minimum1
Maximum
Maximum
Length
11 1/2"
15 inches
Height
6 1/8"
12 inches
Thickness
1/4"
3/4 inch
1 Flats exceed at least one of these dimensions, based on
landscape orientation, unless the flat is an automation
flat which can have a min length of 6", a min height of 5",
and a min thickness of .009".
12" max.
6 1/8" min.
11 1/2" min.
15" max.