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Piece Size Tool: letter or flat, before it costs you
Upload a PDF and the tool measures the finished print size and tells you whether the piece mails as a USPS letter or a flat. It uses the same TrimBox-aware sizing our prepress does, so the answer matches what production would say.
How the size is detected
- TrimBox present: uses the TrimBox as the final piece size. This is the most reliable indication and is what production uses.
- No TrimBox: uses the visible page size. If your PDF includes a 0.125″ bleed and no TrimBox, the reported size will be 0.25″ larger than the final trim in each dimension. We flag this case so you can confirm.
- Multi-page PDFs: only page 1 is measured. Upload the front side or first sheet.
USPS size categories
| Category | Size |
|---|---|
| Letter | At most 6.125″ tall and 11.5″ long. Postcards are letters at a special price: retail (single-piece) cards run 3.5″-4.25″ tall by 5″-6″ long; since July 12, 2026 presorted / automation First-Class cards may run up to 6″ × 9″ when they meet USPS thickness and automation requirements. |
| Flat | Exceeds letter limits in at least one dimension but no dimension exceeds 12″ × 15″. |
| Non-standard | Smaller than the letter minimum (3.5″ × 5″) or larger than the flat maximum (12″ × 15″). Mails as a parcel or non-machinable piece. |
Size decides the postage rate, and a quarter inch is the difference between a letter and a flat. If it comes back a flat, price it that way in the list builder.
Planning a mailing?
Send us the piece and the quantity. Postage is usually the largest line on a mailing, and it is decided before anything prints. We will tell you what your piece actually qualifies for.