The most common postcard dimensions are 4 × 6 inches. This is the industry default because it meets USPS postcard-rate requirements, prints cost-effectively, and works for most marketing campaigns. Other popular postcard sizes include 5 × 7 inches, 6 × 9 inches, and 8.5 × 11 inches, but these require higher postage because they exceed standard postcard-size limits.
This guide breaks down every standard, jumbo, and custom postcard dimension, plus the USPS rules that decide your mailing cost.
USPS Standard Postcard Dimensions (Minimum and Maximum)
The United States Postal Service sets strict rules for what counts as a mailable postcard at the lowest rate. To qualify for First-Class postcard postage, your card must be:
- Rectangular in shape
- At least 3.5 inches high by 5 inches long
- No larger than 4.25 inches high by 6 inches long
- Between 0.007 inches and 0.016 inches thick
Anything smaller, larger, or thinner than these limits gets reclassified and mailed at the higher letter rate instead. This is a hard rule, not a guideline — USPS mail-processing equipment is calibrated to these exact dimensions.
more Posts:Twin Bed Dimensions: The Complete Size Guide (Inches & Feet)
Postcard Dimensions by Category
Standard Postcard Dimensions (4×6, 5×7)
Standard-size postcards cover the 4×6 and 5×7 range. These are the workhorses of direct mail marketing — sales flyers, appointment reminders, real estate promotions, and event invites almost always use one of these two postcard dimensions.
Jumbo Postcard Dimensions (6×9, 6×11, 8.5×11)
Jumbo postcard dimensions start at 6×9 inches and go up to 8.5×11 inches. These larger formats stand out in a mailbox and give room for bold headlines, big photography, or multiple offers on one card. All jumbo sizes mail at the letter rate through.
Mini Postcard Dimensions (for Inserts and Handouts)
Mini postcard dimensions, often around 2.75×4.25 inches, work well for packaging inserts, loyalty cards, and thank-you notes. These smaller postcard dimensions aren’t usually mailed alone — they’re tucked into boxes, bags, or handed out in person. Their small size keeps the message tight: one offer, one call to action, nothing more.
More Posts:Full Bed Dimensions: Size Chart, Room Fit & Buying Guide
Postcard Dimensions and USPS Mailing Rules
Postcard Rate vs. Letter Rate Dimensions
Only postcard dimensions between 3.5×5 and 4.25×6 inches qualify for the discounted postcard rate. Anything bigger — including the popular 5×7 — is billed as a letter, which typically costs more per piece. This single rule is why 4×6 remains the default choice for high-volume mailers.
USPS Marketing Mail Postcard Dimensions
USPS Marketing Mail works differently. There’s no separate discounted postcard rate under this service — every piece is priced like a letter, regardless of postcard dimension, as long as it stays under 6.125×11.5 inches. This gives Marketing Mail senders more size flexibility, since a bigger card doesn’t cost extra compared to a smaller one within that range. Go beyond 6.125×11.5 inches, and the piece is reclassified as a flat, triggering a higher price tier.
Postcard Thickness Requirements by Dimension
Size isn’t the only factor — thickness matters too. USPS requires a minimum of 0.007 inches and a maximum of 0.016 inches for postcard-rate eligibility. A helpful comparison: an average index card is roughly this thick.
How to Choose the Right Postcard Dimensions
Postcard Dimensions by Use Case (Marketing, Events, Real Estate)
- Marketing promotions: 4×6 keeps cost low for high-volume sends
- Event announcements: 5×7 or 6×9 gives room for dates, maps, and RSVP details
- Real estate marketing: Jumbo dimensions (6×9 or larger) showcase property photos clearly
- Thank-you or loyalty cards: Mini or 4×6 dimensions keep the touch personal
Postcard Dimensions by Budget and Mailing Volume
For high-volume campaigns, smaller postcard dimensions paired with gang-run printing keep per-piece costs down.
For smaller, targeted mailings, the postage savings from a compact size matter less, so brands often size up for stronger visual presence.
As a rule of thumb: match your postcard dimension to your mailing volume, not the other way around.
More Posts:Twin XL Bed Dimensions: The Complete Size Guide for 2026
FAQs About Postcard Dimensions
What is the standard postcard dimension?
The standard postcard dimension is 4×6 inches. It’s the most commonly used size because it fits USPS postcard-rate requirements and is affordable to print in bulk.
What postcard dimensions qualify for USPS postcard rate?
Postcards must measure between 3.5×5 inches and 4.25×6 inches, with a thickness of 0.007 to 0.016 inches, to qualify for the discounted postcard rate.
Can a 5×7 postcard use postcard-rate postage?
No. A 5×7 postcard dimension exceeds the postcard-rate size limit and is always mailed at the letter rate instead.
What are jumbo postcard dimensions?
Jumbo postcard dimensions range from 6×9 inches up to 8.5×11 inches. These larger formats always mail at the letter rate through USPS.
What postcard dimensions are best for direct mail marketing?
For most direct mail campaigns, 4×6 inches offers the best balance of low cost and message clarity. Larger dimensions like 5×7 or 6×9 work better when visual impact matters more than mailing cost.
How thick should a postcard be for mailing?
A mailable postcard should be between 0.007 and 0.016 inches thick to qualify for postcard-rate postage and move safely through USPS sorting equipment.
James Walker is a content researcher and writer specializing in dimensions, measurements, size comparisons, and conversion topics. He creates clear, practical, and easy-to-understand guides that help readers visualize and understand real-world measurements.