Quick answer: an EDDM mailer must be a USPS Marketing Mail flat — bigger than a letter in at least one dimension. That means longer than 10.5", or taller than 6.125", or thicker than 0.25". It also has to stay within 15" × 12" × 0.75" and weigh 3.3 oz or less at the Post Office. That's why the classic EDDM postcard is 6.5" × 9" — and why a standard 4" × 6" postcard gets rejected at the counter.
Last updated: June 2026. Rules from the official USPS EDDM Quick Reference Guide.
The One Rule That Matters: It Has to Be a "Flat"
USPS sorts mail into letters, flats, and parcels. EDDM only accepts flats — pieces too big to be a letter, but still flat enough to ride in a mail tub. Your piece qualifies when it's rectangular (square counts as a rectangle in USPS rules) and exceeds at least one of the letter maximums while staying within all of the flat maximums:
| Dimension | Must exceed at least one | Cannot exceed any |
|---|---|---|
| Length (always the longest side) | more than 10.5" | 15" |
| Height | more than 6.125" | 12" |
| Thickness | more than 0.25" | 0.75" |
Two more fine-print numbers from the same USPS guide: minimum thickness is 0.007" (about three sheets of copy paper — so card stock, not printer paper) and minimum height is 3.5". Corners can be rounded, but only up to a 0.125" radius.
Sizes That Qualify — and the Trap Sizes That Don't
Here's the part that surprises people: some "normal" postcard sizes don't qualify, because they're letter-sized — and EDDM doesn't take letters.
| Size | EDDM-eligible? | Why |
|---|---|---|
| 6.5" × 9" postcard | Yes | Height beats 6.125" — the most popular EDDM size |
| 6.25" × 11" postcard | Yes | Beats both the height and length minimums |
| 8.5" × 11" oversized postcard | Yes | Big mailbox presence; USPS lists it as a popular option |
| 4.25" × 14" tri-fold menu | Yes | Length beats 10.5" — restaurant favorite |
| 4" × 6" postcard | No | Letter-sized in every dimension |
| 5" × 7" postcard | No | Still under every flat minimum |
| 6" × 9" postcard | No — the classic trap | 9" is under 10.5" and 6" is under 6.125". A quarter inch short. |
The 6" × 9" trap is the one we catch most often. It looks like an EDDM size, plenty of printers will happily sell it to you, and the Post Office will reject the whole mailing. Check any size in seconds with our free EDDM size checker, or send it to us before you print — we verify it against the USPS rules for free as part of our EDDM quoting.
Weight Limits: Retail vs. BMEU
- EDDM Retail (dropped at your local Post Office): each piece must weigh 3.3 oz or less. No permit needed, up to 5,000 pieces per ZIP per day.
- EDDM BMEU (entered through a Business Mail Entry Unit under a Marketing Mail permit): pieces can weigh up to just under 16 oz, with postage varying by weight. This is the route for heavy multi-page pieces and big drops.
For most postcards and menus, 3.3 oz is plenty — even an 8.5" × 11" on thick stock comes in well under it. We cover the full Retail-vs-BMEU decision in its own chapter of this guide.
Why Bigger Usually Wins
Here's the math most owners miss: EDDM Retail postage is a flat $0.247 per piece whether you mail a 6.5" × 9" postcard or a 12" × 15" poster, as long as it qualifies and stays under 3.3 oz (current USPS rate). The postage doesn't care about size — only the print cost changes, and not by as much as you'd think on a gang run.
So when the budget allows, we usually push clients toward the 8.5" × 11": it's physically the biggest thing in the mailbox that day, it can't hide behind envelopes, and the extra canvas fits a menu, a coupon block, or a before/after photo set. Price the difference yourself on our postcard printing page or with a free itemized quote.
Want the real number for your neighborhood? Our free postage calculator prices your routes in minutes — and postage at Catdi Printing is always a pass-through. You pay exactly what USPS charges, never a markup.
EDDM Size FAQ
Can I mail a standard 4" × 6" or 6" × 9" postcard with EDDM?
No. Both are letter-sized under USPS rules, and EDDM only accepts flats. The smallest common EDDM-eligible postcard is 6.25" × 9" — most shops, including ours, print 6.5" × 9" as the entry size.
Does a bigger EDDM piece cost more postage?
No — that's the beauty of it. Every qualifying piece up to 3.3 oz mails at the same $0.247 EDDM Retail rate. Only your print cost changes with size.
Can my EDDM piece be a folded menu or brochure?
Yes, as long as the folded piece meets the flat dimensions — the 4.25" × 14" tri-fold menu is one of the three most popular EDDM formats in USPS's own fact sheet. Folds should be on the final (bottom) edge for clean machine handling.
Can an EDDM mailer be square?
Technically yes — USPS counts a square as a rectangle — but it still has to beat one of the flat minimums, so you'd need a square bigger than 6.125" per side. A 7" × 7" qualifies; a 6" × 6" doesn't.
What happens if my piece is the wrong size?
The Post Office refuses the mailing at acceptance — after you've already paid for printing. That's the expensive way to learn the rules, and it's why we size-check every EDDM file before it touches a press.
Get Your Size Right Before You Print
Send us the piece you have in mind — size, stock, fold — and we'll confirm it qualifies, price the print run, and estimate the postage for your exact routes, itemized so you can see every line. Start with an EDDM quote, explore our EDDM service, or call (713) 882-4629 — a Houston print rep picks up, not a phone tree.