USPS Postcard Size Requirements and Mailing Guidelines

Postcards are commonly used for direct mail campaigns, announcements, promotions, and customer follow-ups. Before printing, make sure your postcard size, shape, thickness, and mailing layout are suitable for USPS mailing.

Quick Answer

To qualify for standard USPS postcard mailing rates, a postcard generally needs to be:

• Rectangular

• At least 3.5" high × 5" long

• No more than 4.25" high × 6" long

• Between 0.007" and 0.016" thick

• Designed with enough space for the address, postage, and postal markings

Larger postcards can still be mailed, but they may be priced as letters, flats, or another mail category. Always confirm the final requirements before printing a large mailing order.

Common Postcard Sizes

Common postcard sizes include:

• 4" × 6"

• 5" × 7"

• 5.5" × 8.5"

• 6" × 9"

• 6" × 11"

A 4" × 6" postcard is often used when customers want a compact size that may fit standard postcard mailing guidelines.

Larger sizes offer more design space, but they may not qualify for the same postage rate.

Size, Shape, and Thickness

For standard postcard eligibility, the card should generally be rectangular. Square, die-cut, round, folded, or unusually shaped pieces may require different postage or special handling.

When choosing your postcard, consider:

• Final size

• Cardstock thickness

• Shape

• Paper finish

• Mailing method

• Whether the card will be mailed individually or as part of a campaign

If mailing cost is important, confirm the size and mail class before finalizing your artwork.

Mailing Side Layout

The mailing side should leave enough clear space for postal processing.

Make sure your design includes room for:

• Recipient address

• Return address, if used

• Postage, stamp, or mailing indicia

• Barcode or postal marking area

Avoid placing QR codes, logos, important text, or promotional messages too close to the address area or postal clear zones.

A clean mailing side helps reduce the risk of scanning issues, delays, or returned mail.

Design Tips for Mailed Postcards

A postcard needs to work as both a marketing piece and a mail-ready item.

For better results:

• Keep the address area clean and readable

• Use high contrast for important text

• Leave space around postal areas

• Keep QR codes away from postal markings

• Keep important details away from trim edges

• Check dates, phone numbers, prices, and website links carefully

If your postcard includes a special offer or event date, review the details before ordering.

Common Mistakes to Avoid

Avoid these common issues:

• Choosing a size without checking mailing eligibility

• Assuming all postcard sizes qualify for the same mailing rate

• Using a square, folded, or die-cut shape without checking postage rules

• Placing important content in the address or barcode area

• Making contact information too small to read

• Printing a large quantity before confirming USPS requirements

A postcard can look good visually but still create mailing problems if the size, thickness, or address layout is not planned correctly.

Final Check Before Ordering

Before printing, check:

• Is the postcard size suitable for your mailing plan?

• Does the card meet the required shape and thickness guidelines?

• Is there enough room for the address and postage?

• Are important design elements away from postal processing areas?

• Are all dates, addresses, phone numbers, prices, and QR codes correct?

• Have you confirmed the requirements for your chosen mail class?

For large direct mail campaigns, confirm the final size, paper stock, and mailing layout with USPS or your mailing service before printing.