201c Quick Service Guide

Physical Standards for Commercial Flats



Flat Dimensions

Flat dimensions. Image shows minimum and maximum size for flats.





11-1/2 inches

15 inches


6-1/8 inches

12 inches


1/4 inch

3/4 inch

* Flats exceed at least one of these dimensions

For physical standards of automation flats, see Quick Service Guide 201d.

In addition to shape, the Postal Service classifies mailpieces by the way they are prepared. These classifications are based on how efficiently your mailpieces can be processed on Postal Service equipment. The Postal Service classifies commercial flats as either nonautomation or automation flats or machinable and nonmachinable for Periodicals.

A flat meets automation standards and qualifies for automation prices if it meets the specific addressing, barcoding, and design standards. Automation flats must have an Intelligent Mail barcode with a delivery point routing code.

Dimensions, Shape, Flexibility, and Uniform Thickness (201.4.0)


The length of a flat-size mailpiece is the longest dimension. The height is the dimension perpendicular to the length.

Shape: rectangular, with four square corners, or with finished corners that do not exceed a radius of 0.125 inch (1/8 inch).

Flexibility and deflection: flat-size pieces must meet flexibility criteria in 201.4.3 and the deflection criteria in 201.4.6. Flat-size pieces mailed at high density, high density plus, saturation, and basic carrier route prices are not required to meet deflection standards. All other flats not meeting deflection standards are subject to prices as stated in DMM 201.4.7.

Uniform thickness: the contents must be uniformly thick so that any bumps, protrusions, or irregularities do not cause more than 1/4 inch variance in thickness (201.4.4). When determining variance in thickness, exclude the outer edges of a mailpiece (1 inch from each edge) when the contents do not extend to the edges.

Mailpieces that do not meet the standards for flexibility in 201.4.3, for uniform thickness in 201.4.4, or for polywrap in 201.4.5, must pay applicable prices as follows:

Presorted Nonautomation Flats (201.5.0)

Maximum weight:

Automation Flats (201.6.0)

Flats may qualify for the automation discount based on the physical standards in 201.6.0.

See Quick Service Guide 201d, Designing Flats for Automated Processing, for an overview.

Quick Service Guides

First-Class Mail

See Quick Service Guides:

230d Nonautomation Flats

230e Automation Flats

USPS Marketing Mail

See Quick Service Guides:

240e Nonautomation Flats

240f Automation Flats

240g Carrier Route Flats

Bound Printed Matter

See Quick Service Guide:

260a Flats

Media Mail and Library Mail

See Quick Service Guide:

270a Presorted Flats


See Quick Service Guides:

207d Nonmachinable Flats

207f Barcoded (Automation) Flats