Direct Mail Postcard Sizes: USPS Requirements & Best Practices

Choosing the right postcard size affects postage cost, mailbox visibility, and response rates. This guide covers all standard USPS postcard sizes, postage rates for each, and recommendations for different campaign types.

USPS Postcard Size Categories

Standard postcards (letter-size): Minimum 3.5" × 5", maximum 4.25" × 6". Qualifies for First-Class postcard rate ($0.56 retail, $0.48 metered, lower with presort).
Large postcards (letter-size): 4.25" × 6" to 6.125" × 11.5". Qualifies for First-Class letter rate or Marketing Mail letter rate.
Flat-size postcards: Minimum 6.125" × 11.5", maximum 12" × 15". Required for EDDM. Qualifies for Marketing Mail flat rate or EDDM Retail ($0.260/piece).

Common Postcard Sizes

4" × 6": Most affordable to mail. Good for appointment reminders, thank-you cards, and simple announcements.
5" × 7": More design space. Good for event invitations and product announcements.
6" × 9": Oversized — stands out in the mailbox. Good for retail promotions and real estate.
6" × 11": Maximum letter-size. High visibility with room for detailed messaging.
6.25" × 11.5" (EDDM minimum): Required minimum for EDDM campaigns. Lowest per-piece postage for saturation mailings.
8.5" × 11": Full-page flat. Maximum design space for menus, maps, and detailed promotions.
9" × 12": Large flat. Premium format for high-impact campaigns.

Size Selection Guide

Budget priority: 4×6 standard postcard (lowest postage)
Visibility priority: 6×9 or 6×11 oversized (stands out in mailbox)
EDDM campaigns: 6.25×11.5 minimum (required for EDDM pricing)
Maximum impact: 8.5×11 or 9×12 flat (most design space)

Design Requirements

Address panel: minimum 4" wide × 2" tall on the right half of the back
Barcode clear zone: 4.5" × 0.625" at bottom of address side
Return address: upper left corner of address side
Postage area: upper right corner of address side

Postcard Printing | EDDM Services | Get a Quote

What is the standard postcard size? The standard postcard size for mailing in the United States is 4.25" × 6" (or 4" × 6"), which qualifies for the lowest USPS postcard postage rate. However, postcard dimensions for direct mail campaigns range from the minimum 3.5" × 5" up to oversized flats at 12" × 15". This guide covers every USPS postcard size, dimension requirements, aspect ratio rules, and postage rates — so you can choose the right size for your campaign goals and budget.

Quick Answer

The most popular direct mail postcard size is the 6×9" oversized postcard — it qualifies for USPS Marketing Mail flat rates, stands out in the mailbox, and offers ample design space. Standard postcards (4×6") are the most affordable option. EDDM-compliant flats require a minimum size of 6.125×11.5". Postcard size determines both postage class and printing cost, so choosing the right size is one of the most important campaign decisions.

Direct Mail Postcard Sizes at a Glance

Size Name	Dimensions	USPS Class	Approx. Postage	Best For
Standard Postcard	4" x 6" or 4.25" x 6"	First-Class Postcard	~$0.56	Budget campaigns, quick announcements
Large Postcard	5" x 7" or 5.5" x 8.5"	First-Class Letter or Marketing Mail	~$0.82–$0.395 (eff. July 2026)	Promotions, coupons, event invitations
Jumbo Postcard	6" x 9"	Marketing Mail Flat	~$0.228	Most popular; high impact, affordable
Oversized Postcard	6" x 11" or 8.5" x 11"	Marketing Mail Flat	~$0.228	Maximum visibility; real estate, home services
EDDM Standard	6.5" x 9" or 6" x 11"	EDDM Marketing Mail	~$0.260	Neighborhood saturation campaigns
EDDM Large	8.5" x 11" or 9" x 12"	EDDM Marketing Mail	~$0.260	Maximum EDDM impact; restaurants, retailers

* Postage rates as of 2026. Marketing Mail rates shown are for presorted pieces. First-Class rates shown are for single-piece. Contact us for exact rates for your mailing.

The Most Popular Sizes — Explained

4" x 6" Standard Postcard

Lowest postage

Pros

Lowest postage rate (USPS postcard rate)
Lowest printing cost
Fast turnaround
Good for simple offers and announcements

Cons

−Smallest canvas — limited design space
−Less visible in a full mailbox
−Lower response rates than larger sizes for most campaigns

Best for: Budget campaigns, quick announcements, appointment reminders, simple coupon offers

6" x 9" Jumbo Postcard

6" x 11" or 8.5" x 11" Oversized Postcard

Highest impact

Pros

Maximum visibility in the mailbox
Most design space for compelling imagery and copy
Qualifies for EDDM
High perceived value — recipients are less likely to discard

Cons

−Highest printing cost per piece
−Requires more postage than standard sizes (flat rate vs. letter rate)

Best for: Real estate listings, home services, restaurant menus, high-value offers, EDDM campaigns

USPS Postcard Dimensions & Aspect Ratio Requirements

USPS has specific postcard dimension requirements that determine your mail class, postage rate, and whether your piece qualifies for automation discounts. The postcard aspect ratio (length ÷ height) must fall between 1.3 and 2.5 for automation-compatible rates. Here are the official USPS postcard size rules:

Minimum size

3.5" x 5" — pieces smaller than this are not mailable

Maximum postcard rate size

4.25" x 6" — pieces larger than this are classified as letters or flats

Minimum thickness

0.007" — pieces thinner than this may not process through automation equipment

Maximum thickness (letter)

0.25" — thicker pieces are classified as parcels

Aspect ratio (critical)

Length ÷ height must be between 1.3 and 2.5. Example: a 6×9 postcard = 9÷6 = 1.5 (valid). A 6×6 square = 1.0 (invalid — surcharge applies)

Address placement

Address must be in the lower right quadrant of the address side, with a clear zone for barcoding

Return address

Required for Marketing Mail to receive undeliverables; strongly recommended for all classes

Tabbing (self-mailers)

Folded self-mailers must be tabbed (wafer sealed) on the open edge — we handle this

We review all artwork against USPS specifications before printing. If your design has issues, we'll catch them before they cause delays or surcharges.

Frequently Asked Questions

Standard postcards (up to 4.25" x 6") qualify for the lowest USPS postage rate — currently around $0.56 for First-Class or $0.194 for Marketing Mail. However, larger postcards (4.25" x 11" or 6" x 9") often get higher response rates because they're more visible in the mailbox, which can make them more cost-effective on a cost-per-response basis even though they cost more to mail.

The 6" x 9" postcard is the most popular size for direct mail campaigns. It's large enough to make an impact, qualifies for Marketing Mail rates (not First-Class), and fits standard USPS automation equipment. The 4.25" x 6" standard postcard is the most popular for budget-conscious campaigns.

USPS defines a postcard as a piece that is at least 3.5" x 5" and no larger than 4.25" x 6". Pieces larger than 4.25" x 6" are classified as letters or flats and are subject to different postage rates. However, larger pieces can still be mailed at Marketing Mail rates — they just don't qualify for the postcard rate specifically.

EDDM requires a minimum size of 3.5" x 5" and a maximum size of 15" x 12". The most popular EDDM sizes are 6.5" x 9", 8.5" x 11", and 6" x 11". Larger EDDM pieces (8.5" x 11" and up) tend to get higher response rates because they stand out in the mailbox, and the EDDM flat rate applies regardless of size.

A return address is not required by USPS for postcards, but it's strongly recommended. Without a return address, you won't receive undeliverable pieces back, which means you can't clean your list. For Marketing Mail, pieces without a return address are discarded by USPS rather than returned.

The standard postcard size for mailing in the US is 4.25" x 6" (or 4" x 6"). This is the maximum size that qualifies for the USPS postcard postage rate. Anything larger is classified as a letter or flat and requires higher postage. The minimum mailable postcard size is 3.5" x 5".

USPS requires postcards to be between 3.5" x 5" (minimum) and 4.25" x 6" (maximum for postcard rate). The aspect ratio (length divided by height) must be between 1.3 and 2.5 to qualify for automation rates. Pieces outside this ratio incur a nonmachinable surcharge. Minimum thickness is 0.007" (7pt cardstock).

Standard postcards are 4" x 6" or 4.25" x 6" in inches. Large postcards are typically 5" x 7" or 5.5" x 8.5". Jumbo postcards (most popular for direct mail) are 6" x 9". Oversized postcards range from 6" x 11" to 9" x 12". EDDM-compliant pieces must be at least 6.125" x 11.5" or larger.

Ready to Print Your Postcards?

We print and mail postcards in all standard sizes. Get a free quote and we'll recommend the best size for your campaign goals and budget.