Standard Postcard Sizes and What Each Costs to Mail

Most size guides tell you a postcard is 4x6 and leave it there. That's half the answer. The other half is what each size costs to mail, because the Post Office sorts every card into a different price bucket based on its dimensions, and a size that's only an inch bigger can cost you a lot more. So here are the standard postcard sizes, the USPS class each one lands in, and what it costs to mail today, whether you're sending ten thank-you cards or 5,000 ads to a neighborhood.

Standard postcard sizes at a glance

Here's the thing. Printers sell about eight sizes over and over. Each one falls into one of three USPS buckets: postcard, letter, or flat. The bucket sets the price.

Size (inches)	Common name	USPS class with a stamp	Stamped price	EDDM Retail price
4 x 6	Standard postcard	Postcard	$0.65	Doesn't qualify
4.13 x 5.83 (A6)	International standard	Postcard	$0.65	Doesn't qualify
5 x 7	Medium	Letter	$0.82	Doesn't qualify
5.5 x 8.5	Half-letter	Letter	$0.82	Doesn't qualify
6 x 9	Large	Letter	$0.82	Doesn't qualify
6 x 11	Jumbo	Letter	$0.82	$0.26
8.5 x 11	Full-page	Flat	$1.69	$0.26
9 x 12	Oversized	Flat	$1.69	$0.26

All prices in this post come from USPS Notice 123, checked October 31, 2026. Stamped prices are for the first ounce. Prices change, so check before you buy a roll of stamps.

Two rows should jump out at you. The 6x9 doesn't qualify for EDDM, even though one popular size guide says it does. And the 6x11 has two prices depending on how you mail it. I'll explain both below.

The A6 size is the international one, 105 x 148 mm (papersizes.org), so it lands in the same bucket as a 4x6 in the U.S. And those cute 4x4 square cards some printers sell? They're under the USPS minimum of 5 inches long, so they can't go in the mail on their own. Put them in an envelope.

USPS postcard size: the 4x6 rule

To USPS, a "postcard" is a specific thing. For the postcard stamp price, a card has to be (DMM 101.6.2.2):

• At least 3.5 inches high, 5 inches long, and 0.007 inch thick
• No more than 4.25 inches high, 6 inches long, and 0.016 inch thick
• Rectangular

That's it. The USPS postcard size tops out at 4.25 x 6. A 4x6 fits with a little room. A 5x7 does not, and neither does anything bigger.

That's the retail postcard stamp, $0.65 as of October 31, 2026.

In plain English: if it's bigger than 4.25 x 6 in either direction, it isn't a postcard to USPS, no matter what the printer calls it.

The thickness trap

Paper thickness is measured in points, and one point is 0.001 inch. So 14 pt stock is 0.014 inch and 16 pt is 0.016 inch, right at the ceiling. Point sizes are nominal and real stock varies a bit, so if you're on 16 pt, ask your printer for the actual thickness. Order a super-thick "luxury" 4x6 on heavier stock than that and USPS no longer treats it as a postcard, so the postcard price is off the table. Pretty card. Wrong bucket.

Postcard dimensions bigger than 4x6: letters

Once a card is bigger than 4.25 x 6, USPS mails it as a letter, as long as it stays within letter size. Letter size maxes out at 11-1/2 inches long, 6-1/8 inches high, and 1/4 inch thick (DMM 101.1.1). Pieces more than 6 inches long or 4.25 inches high also need to be at least 0.009 inch thick.

So the 5x7, the 5.5x8.5, the 6x9, and even the 6x11 are all letters when you stamp them. Each one costs the 1-ounce letter price: $0.82 with a stamp, or $0.78 if you use a postage meter. That's 13 to 17 cents more than a 4x6 for the exact same trip to the mailbox.

In plain English: bigger than a 4x6 but no more than 6-1/8 inches high and 11-1/2 inches long, it's a letter.

Square cards cost even more

Square postcards look great on Instagram. In the mail, not so much. USPS calls a letter "nonmachinable" if its length divided by its height is under 1.3 or over 2.5 (DMM 101.1.2). A square card is 1.0. So a 5x5 card is a letter (it's too tall to be a postcard) AND it's nonmachinable:

• $0.82 letter price
• plus the $0.49 nonmachinable surcharge
• $1.31 per card

Twice the price of a 4x6. For a wedding invite, sure. For a marketing mailer, that's a tough sell.

Why some sites say postcards can be 6x9

You'll see pages claim the postcard rate goes up to 6x9. They're mixing up two different rulebooks. The 6 x 9 limit is real, but it's in USPS's commercial rules (DMM 201.1.2.1), which cover presorted commercial First-Class mailings. That's mailing-house territory. If you walk into the Post Office with a stamp, the ceiling is 4.25 x 6. Full stop.

Flats: the big cards

Go past letter size and you're in flat territory. A flat is more than 11-1/2 inches long, or more than 6-1/8 inches high, or more than 1/4 inch thick, and no bigger than 15 x 12 x 0.75 inches (DMM 101.2.1). Large envelopes, catalogs, and big postcards.

So a 9x12 is a flat. So is an 8.5x11. So is a 6.25x9, because 6.25 inches high is over the 6-1/8 letter limit.

Mail a flat one at a time with stamps and it's the large envelope price: $1.69 for the first ounce, and $1.98 at 2 ounces. That's why nobody mails big cards with stamps. Honestly, it would be crazy.

Every Door Direct Mail: where big cards get cheap

Here's where it flips. Every Door Direct Mail (EDDM) Retail lets you mail to every address on a carrier route with no mailing list and no permit, and it charges $0.26 per piece for flats up to 3.3 ounces, as of October 31, 2026. One price, whether the card is 6x11 or 12x15.

EDDM Retail takes flats only, but it uses its own size test. A piece qualifies if it's longer than 10.5 inches, OR taller than 6.125 inches, OR thicker than 0.25 inch, up to 15 x 12 x 0.75 and 3.3 ounces (DMM 143). Pass one test and you're in. I go through every common size, folding, and vertical designs in the EDDM size requirements post, so I won't repeat all of it here.

What matters for this post:

• 4x6, 5x7, 5.5x8.5, 6x9: fail all three tests. Not EDDM.
• 6x11: 11 inches beats 10.5 on length. EDDM Retail flat, $0.26. But stamp it and it's a letter at $0.82. Same card, two prices, depending on how you mail it.
• 8.5x11 and 9x12: pass on length and height. $0.26.

And EDDM has a 200-piece minimum per mailing, not per route. So it's for neighborhoods, not your Christmas card list. It also comes in a permit version for bigger mailers, covered in EDDM Retail vs BMEU. If you're new to it, how EDDM works covers the basics.

What it costs to mail 5,000 cards, by size

Okay so let me break it down with real numbers. Same 5,000 homes, postage only, no printing:

That's 5,000 times $0.65, $0.82, $1.69 (one ounce), and $0.26.

Read that again. The biggest card costs the least to mail, as long as you mail it the right way. The little 4x6 everybody calls "standard" costs two and a half times as much in postage to reach the same houses, and you'd also need every name and address.

The size everybody calls standard is the one that costs the most to put in every mailbox on the street.

That's not a knock on 4x6. For a personal note, a thank-you to a customer, or a mailing list of 80 past clients, a 4x6 with a stamp is perfect. It's just the wrong tool for hitting a whole neighborhood.

Postcard size guide: which size should you pick?

Here's my simple postcard size guide, based on what you're actually doing:

• Mailing a handful to people you know by name? Go 4x6 and use postcard stamps. The lowest price per card for small batches.
• Want a bit more room but still mailing to a list? 5x7 or 6x9 works. Budget the $0.82 letter price, not $0.65.
• Hitting a whole neighborhood (200 pieces or more)? Pick a size that passes the EDDM test, like 6x11, 8.5x11, or 9x12, and mail at $0.26.
• Splitting the card with other local businesses? Go as big as you can. On a shared card, size is your inventory.

It is that simple. Then, before you print anything, run the same three checks every time:

1. Measure the finished card, trimmed (and folded, if it folds) the way it will go in the mail.
2. Check the thickness against your mail class (0.016 inch max for a postcard).
3. Check the shape. Length divided by height under 1.3 means a square-card surcharge on letters.
4. Make sure the word "Postcard" isn't printed on a card that isn't one.

Why we mail the biggest one

Full transparency, I'm biased here. The whole 9x12 Method is built on the big card. As I always say, it's the "biggest thing anybody ever receives in their mailbox." Then you sell 16 ad slots on it to local businesses for about $500 each.

Here's a fun way to picture it. A standard ad slot on our 9x12 is about 3.8 x 2.8 inches. A double slot is 4x6. So a whole "standard postcard" is just one double slot on our card. Sixteen businesses share a card where a single 4x6 would be one ad.

And businesses buy those 4x6 doubles. Michael sold 10 slots before noon one morning, all from email and calls (his card used 2x3, 4x3, and 4x6 spots): three 2x3s, six 4x3s, and one 4x6. Another time he filled an empty 4x6 spot with a Mexican restaurant in 10 minutes to hit a print deadline. Leland had two clients take double slots at $900 each on his very first card.

The numbers on the two cards we run:

Metric	Value
9x12 card revenue (16 x $500)	$8,000
9x12 All Inclusive to 5,000 homes	$2,999
9x12 profit	$5,001
6x11 community card revenue (16 x $250)	$4,000
Community card All Inclusive to 2,500 homes	$1,449
Community card profit	$2,551

All Inclusive with 9x12 Method Printing means 14 pt UV gloss cards, printed, bundled, with the EDDM postage included, shipped to the Post Office. For the smaller format, here's community card printing, and if you're deciding between them, read 9x12 vs community card first. Most beginners start with what a community card is and go from there.

I teach slot sizes, layouts, and pricing inside the 9x12 Method community. You don't need it to pick a size, though. The table at the top of this post is honestly all you need.

Frequently Asked Questions

What is the standard postcard size in the US?

4 x 6 inches. It fits inside the USPS postcard limits (3.5 x 5 up to 4.25 x 6 inches, 0.007 to 0.016 inch thick), so it mails at the postcard stamp price, $0.65 as of October 31, 2026.

Can I mail a 5x7 postcard with a postcard stamp?

No. A 5x7 is bigger than the 4.25 x 6 postcard maximum, so USPS treats it as a letter. With a stamp that's $0.82 for one ounce as of October 31, 2026.

How much does it cost to mail a 6x9 postcard?

At the counter or with stamps, a 6x9 is a letter: $0.82 as of October 31, 2026. It does not qualify for EDDM Retail, because 9 inches isn't over 10.5 and 6 inches isn't over 6.125. Presorted commercial mailings through a mail house can get card prices on cards up to 6x9.

Do square postcards cost more to mail?

Yes. A square card is nonmachinable because its length divided by its height is under 1.3. A 5x5 card pays the $0.82 letter price plus a $0.49 surcharge, $1.31 total as of October 31, 2026.

What size postcard qualifies for EDDM?

One that's longer than 10.5 inches, taller than 6.125 inches, or thicker than 0.25 inch, and no bigger than 15 x 12 x 0.75 inches and 3.3 ounces. 6x11, 8.5x11, and 9x12 all qualify. 4x6, 5x7, and 6x9 don't.

How thick can a postcard be?

For the postcard price, no more than 0.016 inch, which is 16 pt stock, and no thinner than 0.007 inch. Our 9x12 and 6x11 cards are 14 pt, but they're flats, so the postcard thickness limit doesn't apply to them.

Whatever size you go with, I hope this saves you a surprise at the Post Office counter. As always, I'm rooting for you.