USPS mailpiece dimensions
Design the piece around the postage.
Finished size, thickness, weight, orientation and construction determine whether USPS treats a piece as a postcard, letter, flat or parcel. Review the basics before printing so a small design choice does not create a large postage surprise.
Quick classification guide
Postcard, letter or flat?
These are planning dimensions from current USPS commercial design standards. Exact eligibility also depends on flexibility, uniform thickness, address placement, folds, tabs, paper and other construction rules.
Commercial postcard-size
A rectangular, unfolded card prepared for qualifying commercial First-Class Mail card prices.
3.5–6 inches high
0.007–0.016 inch thick
- Cards over 6 inches long or 4.25 inches high must generally be at least 0.009 inch thick.
- Aspect ratio generally must be 1.3–2.5.
Machinable letter-size
Most envelopes, folded self-mailers and smaller cards fall into the letter category when properly constructed.
3.5–6.125 inches high
0.007–0.25 inch thick
- Pieces over 6 inches long or 4.25 inches high generally need at least 0.009-inch thickness.
- Machinable commercial letters may weigh up to 3.5 ounces.
Large envelope or flat-size
A piece becomes flat-size when it exceeds at least one letter maximum while staying within the flat maximums.
12 inches high
0.75 inch thick
- Flats must be rectangular and meet applicable flexibility, rigidity and uniform-thickness standards.
- Different weight limits apply by mail class.
Planning table
Compare the basic dimensional limits.
“Length” is the edge parallel to the address as the piece is designed to travel through postal equipment.
| Category | Length | Height | Thickness | Important note |
|---|---|---|---|---|
| Commercial postcard | 5–9 in. | 3.5–6 in. | 0.007–0.016 in. | Rectangular, unfolded cardstock; additional price and preparation standards apply. |
| Machinable letter | 5–11.5 in. | 3.5–6.125 in. | 0.007–0.25 in. | Aspect ratio generally 1.3–2.5; construction must be automation compatible. |
| Flat | Over 11.5, up to 15 in. | Over 6.125, up to 12 in. | Over 0.25, up to 0.75 in. | Exceeding any one letter maximum can create a flat, provided all flat standards are met. |
| EDDM Retail piece | Must qualify as flat-size | Must qualify as flat-size | Within flat standards | Generally no more than 3.3 oz.; routes, bundles and Retail entry rules also apply. |
Beyond the ruler
Size alone does not guarantee the best rate.
Aspect ratio and orientation
For letter-size automation, divide length by height. A ratio outside 1.3–2.5 can make a piece nonmachinable. Rotating the address can change which edge USPS treats as the length.
Folds, tabs and openings
Folded self-mailers have detailed construction rules. Fold location, panel count, paper weight and tab placement can affect automation eligibility.
Coatings and address areas
Gloss, UV and aqueous coatings can interfere with ink adhesion or barcode contrast. Leave an appropriate uncoated address area or plan for labels.
Weight and uniformity
Uneven inserts, bulky fasteners, clasps, magnets or rigid contents can change machinability even when the outside dimensions appear acceptable.
Before you print
Three steps that prevent expensive surprises.
Send the artwork
Share a PDF showing the finished size, folds, address block, indicia, tabs and coatings.
Provide a physical mockup
For folded or assembled pieces, a sample lets us evaluate thickness, flexibility and machine travel.
Confirm before production
We will identify likely classification issues before the full print run is committed.
Planning guidance, not a postal ruling. USPS standards and prices change, and exceptions apply. Final classification requires review of the finished piece and the mailing plan. Source: USPS Domestic Mail Manual, commercial design standards.
Free preflight help
Let us review the piece before it goes to print.
Send the dimensions, artwork, quantity and mailing date. We will help identify problems while they are still easy to fix.