What Size Is A Post Card? Typical Postcard Size Guide

Postcards make it easy to reach your customers with a personal touch. Because they’re delivered without an envelope, your message is immediately visible the moment someone checks their mailbox. Choosing the right postcard size is the first step to a successful campaign.

The right size of postcard not only impacts the look and feel of your message, but can also affect postage costs and how your card stands out in the mail. Here’s what you need to know about standard postcard sizes and how to pick the perfect fit for your next project.

Ultimate Postcard Size Guide In Inches, Centimeters, Millimeters, And Pixels

Below is a quick reference chart for the most-used postcard sizes, including print-ready dimensions with bleed (edge-to-edge color), and pixel counts for high-resolution artwork.

Size In Inches	Size In CM	Size In MM	Size in pixels*
4.25″ × 6″	10.795 cm × 15.24 cm	107.95 mm × 152.4 mm	1275 × 1800
4″ × 6″	10.16 cm × 15.24 cm	101.6 mm × 152.4 mm	1200 × 1800
5″ × 7″	12.70 cm × 17.78 cm	127 mm × 177.8 mm	1500 × 2100
3.5″ × 5.5″	8.89 cm × 13.97 cm	88.9 mm × 139.7 mm	1050 × 1650
4″ × 4″	10.16 cm × 10.16 cm	101.6 mm × 101.6 mm	1200 × 1200
5″ × 5″	12.70 cm × 12.70 cm	127 mm × 127 mm	1500 × 1500
3″ × 3″	7.62 cm × 7.62 cm	76.2 mm × 76.2 mm	900 × 900
3.5″ × 7″	8.89 cm × 17.78 cm	88.9 mm × 177.8 mm	1050 × 2100

*All pixel values are shown at 300 dpi (press-ready).

What Is Standard Postcard Size?

While there is no official standard size for postcards, when someone says “postcard,” they’re usually talking about 4″ × 6″ or 4.25″ × 6″. These are essentially the average postcard size for mailing in the United States because they qualify for the USPS postcard rate, saving on postage for every card sent.

Beyond those, you’ll find endless options. These are often used for direct mail campaigns that need more space for images or information. Postcard sizes larger than 4.25″ × 6″ mail at higher rates.

Standard postcard front and back with mountain photo and address layout, demonstrating typical postcard size.

Standard vs. Oversized: Which Should You Pick?

‘Standard’ postcard sizes like 4″ × 6″ and 4.25″ × 6″ are cost-effective and widely recognized. They work well for routine mailings, customer thank-yous, appointment reminders, and promotional handouts. You’ll keep postage costs down and production simple.

Oversized postcards (think 5″ × 7″ and larger) are designed to get noticed. With more room for visuals and offers, they stand out in the mail stack, making them a smart pick for special promotions, product launches, or campaigns where a strong visual presence matters.

Keep in mind: these larger sizes fall under letter-rate postage and require slightly thicker paper stock for smooth mailing.

If you’re unsure which is right for your goals, Greener Printer can recommend a postcard size and paper type that balances impact and budget – always with sustainable options.

USPS Postcard Size Requirements

Every postal service sets standards for what counts as a postcard, especially if you want to qualify for the lowest postage rate. For the United States Postal Service (USPS), the requirements are straightforward:

Shape: Cards must be rectangular.
Minimum size: 3.5 inches high x 5 inches long x 0.007 inches thick.
Maximum size: 4.25 inches high x 6 inches long x 0.016 inches thick.

Designing within these limits helps you keep postage costs down. If your postcard falls outside these dimensions, you can still mail it, but it will be charged at a higher letter rate.

Understanding how the USPS measures postcards will help you avoid surprises. The length is the edge parallel to the address, and must be between 5 and 6 inches. The height is perpendicular to the address, and should be between 3.5 and 4.25 inches.

Most postcards use a landscape layout, so the address lines up with the longer side of the card. If your card is addressed this way (even when the front design is vertical), it will meet postal guidelines.

Address and barcode placement tip: Keep a 4″ × 2″ area on the bottom right of the address side clear for mailing info. Avoid dark backgrounds or heavy graphics here.

Direct mail postcard example with event schedule and address area, showing standard postcard dimensions.

What About Mailing Requirements Outside the U.S.?

Every country’s postal system is different. For example, Canada Post accepts a broader range of postcard sizes than the USPS. If you’re sending postcards internationally, always double-check the specific guidelines for your destination country. This helps avoid delays and unexpected costs.

What Size Postcard Is Most Effective?

There isn’t a single best size. Your choice depends on your campaign goals. Here’s how different formats perform:

Square Postcards

If you want to stand out, square postcards offer a unique look and work well for creative brands. Their balanced layout is perfect for bold images or modern designs, and they can mimic social media image shapes. However, square cards don’t qualify for the USPS postcard rate, so postage is usually higher.

Popular sizes: 3″ x 3″, 4″ x 4″, 5″ x 5″

Mini Postcards

These compact cards are smaller than the standard 4″ x 6″ format. Mini postcards print affordably, but typically can’t be mailed alone; they’re best used as box inserts, event handouts, or package branding.

Popular sizes: 3″ x 3″, 4″ x 4″, 3.5″ x 5.5″

Medium Postcards

Medium postcards give you extra room for design without leaving the affordable postage category. These work well for gift certificates, vouchers, and event invitations.

Popular sizes: 4.25″ x 6″, 5″ x 7″

Large and Extra-Large Postcards

Any postcard larger than 5″ x 7″ grabs attention and accommodates more text or big, bold graphics. These formats work well as sell sheets or detailed promotional pieces, but they typically require higher postage. The largest postcard that still qualifies for presorted letter rates is 6″ x 11″.

Sizes: For postcards over 5″ x 7″, request a custom quote.

Long Postcards and Rack Cards

Long postcards (also called rack cards) are designed for displays in high-traffic locations. They’re taller than traditional postcards and are often used for restaurant menus, tourism guides, or event promotions.

Popular sizes: 3.5″ x 7″, 4″ x 9″

Stack of oversized postcards for nonprofit direct mail, illustrating large postcard size and print quality.

What Size Postcards Does Greenerprinter Offer?

Greenerprinter offers a wide range of different postcard and flat card sizes. We offer the typical postcard sizes that are perfect for sending through the mail:

3” x 3”
3.5” x 5.5”
3.5” x 7”
4” x 4”
4” x 6”
4.25” x 6”
5” x 5”
5” x 7”

But you’re not limited to just the standard options. We can also produce more unique sizes that will make your postcards stand out – we even do custom shapes! With a quick custom quote request, we can create postcards in any dimension you can dream up.

Ready to bring your project to life? Greenerprinter offers a full range of sustainable printing options. Explore some of our most popular products:

Book & Booklet Printing

Cards Deck printing

Playing Cards | Flash Cards | Tarot Cards