The short version: Use 6"×9" postcards. They mail at the same $0.43/piece rate as tiny 4"×6" cards but give you 2.25× more space to make your offer impossible to ignore.
Most guides bury this. We're telling you upfront because we've printed and mailed millions of postcards—and watched too many businesses waste money on the wrong size.
The 3 Postcard Sizes Worth Using
4"×6" — The Budget Option
Cost to mail: $0.43/piece
Best for: Appointment reminders, thank-you cards, existing customers
Our take: Fine for simple messages, but you're leaving impact on the table.
6"×9" — The Sweet Spot (Our Recommendation)
Cost to mail: $0.43/piece
Best for: Most marketing campaigns, promotions, prospecting
Our take: Best value in direct mail. Same postage as a 4"×6" but 2.25× the design space.
6"×11" — Maximum Impact
Cost to mail: $0.43/piece
Best for: Real estate, automotive, home services, competitive industries
Our take: When you need to dominate the mailbox.
Notice something? All three cost the same to mail. The 6"×9" gives you more than double the design space of a 4"×6" for identical postage.
This is the single biggest mistake we see: businesses mailing tiny postcards when they could mail bigger ones for the same price.
Here's the math: 5,000 postcards × $0.43 = $2,150 in postage whether you mail 4"×6" or 6"×11". The only difference is your printing cost—and the extra $200-400 in print gets you dramatically more visibility.
USPS Size Requirements
Your postcard must meet these specs or it gets rejected (or reclassified to a higher postage rate):
For letter-rate postage (the $0.43 rate):
Minimum size: 3.5" × 5"
Maximum size: 6.125" × 11.5"
Minimum thickness: 0.007" (0.009" for cards larger than 4.25"×6")
Maximum thickness: 0.25"
Shape: Must be rectangular with aspect ratio between 1.3 and 2.5
Go larger than 6.125" × 11.5" and you pay flat rates—often $1.00+ per piece. That kills your campaign economics.
Thickness matters: Always use 14pt or 16pt cardstock. Thinner stock jams USPS sorting machines and arrives damaged—or not at all.
Which Size Should You Choose?
Use 4"×6" if:
You're reminding existing customers about appointments
The message fits in a tweet
You're testing a concept before scaling up
Budget is extremely tight
Use 6"×9" if (this is what we recommend 80% of the time):
You're prospecting to people who don't know you yet
You want room for a compelling image AND a clear offer
You're running any kind of promotional campaign
You want the best ROI on your mail spend
Use 6"×11" if:
You're in real estate, automotive, or home services
Your audience is 50+ (larger fonts matter)
You have multiple offers or need space for maps and coupons
Competitors are already using oversized mail
Design Specs: Get Your Files Right the First Time
Nothing delays a campaign like incorrect file setup. Here's exactly what your designer needs:
For a 6"×9" postcard:
Final trim size: 6" × 9"
File size with bleed: 6.25" × 9.25"
Safe area (keep text and logos inside this): 5.5" × 8.5"
Bleed: 0.125" on all sides
Resolution: 300 DPI minimum
Color mode: CMYK
For a 6"×11" postcard:
Final trim size: 6" × 11"
File size with bleed: 6.25" × 11.25"
Safe area: 5.5" × 10.5"
Bleed: 0.125" on all sides
Resolution: 300 DPI minimum
Color mode: CMYK
For a 4"×6" postcard:
Final trim size: 4" × 6"
File size with bleed: 4.25" × 6.25"
Safe area: 3.5" × 5.5"
Bleed: 0.125" on all sides
Resolution: 300 DPI minimum
Color mode: CMYK
Address Panel Requirements
USPS machines need specific placement to process your mail automatically:
Address block: Right side of the card, minimum 4" wide × 2" tall
Barcode clear zone: Bottom 0.625" of the card must be free of dark colors, images, or text
Return address: Upper left corner
Postage indicia: Upper right corner
Get this wrong and your mail gets hand-sorted, adding days to delivery and potentially triggering surcharges.
What About EDDM?
Every Door Direct Mail has different rules. Standard 4"×6" postcards don't qualify for EDDM.
EDDM requirements:
Your mailpiece must exceed 6.125" tall OR 11.5" long
Common EDDM sizes: 6.5"×9", 8.5"×11", 9"×12"
Postage runs about $0.20/piece
No targeting by name—only by postal route
EDDM works great for local saturation campaigns (restaurants, retail, home services reaching nearby neighborhoods). For targeted campaigns using a mailing list, stick with standard Marketing Mail.
Frequently Asked Questions
Why not use 5"×7"?
It costs the same to mail as 6"×9" but gives you less space. The math never makes sense, so we don't recommend it.
Does bigger actually perform better?
Yes. We consistently see 15-30% higher response rates on 6"×9" and 6"×11" cards compared to 4"×6". More space means better visuals, which means more attention.
What's the turnaround time?
For standard postcard jobs, we typically print and mail within 5-7 business days. Rush jobs are possible—call us.
Can you handle variable data (personalized postcards)?
Yes. We print names, addresses, unique offers, even personalized maps and images. Variable data typically increases response rates by 30-50%.
Do you help with design?
Yes. Our team can design your postcard or work from your files. Either way, we make sure it meets USPS specs before it goes to press.
What paper stock do you recommend?
14pt or 16pt cardstock with a UV or aqueous coating. This meets USPS thickness requirements, feels substantial to recipients, and protects the print during mail processing.
How many postcards do I need to get bulk rates?
Marketing Mail requires a minimum of 200 pieces. For the best rates, 500+ pieces with presorting and barcoding gets you the deepest discounts.
Postcard Size Comparison
4"×6" Postcard
Surface area: 24 square inches
Postage: $0.43 per piece
Print cost (per 5,000): approximately $350-450
Visibility: Standard
Best for: Simple reminders to existing customers
EDDM eligible: No
6"×9" Postcard
Surface area: 54 square inches (2.25× larger than 4×6)
Postage: $0.43 per piece
Print cost (per 5,000): approximately $500-650
Visibility: High
Best for: Most marketing campaigns
EDDM eligible: Yes (at 6.5"×9")
6"×11" Postcard
Surface area: 66 square inches (2.75× larger than 4×6)
Postage: $0.43 per piece
Print cost (per 5,000): approximately $600-800
Visibility: Maximum
Best for: High-impact offers in competitive industries
EDDM eligible: Yes
Print costs shown are estimates for 14pt cardstock, full color both sides. Your quote may vary based on quantity, paper stock, and finishing options.
Ready to Get Started?
We've been printing and mailing direct mail from Lakeland, Florida since 1989. Veteran-owned, 25 employees, and we actually answer the phone.
Call us: (863) 687-6945
Talk to someone who knows direct mail—not a phone tree.
Get a quote: mailpro.org/request-a-quote
Tell us what you're planning. We'll send real numbers within 24 hours.
Schedule a consultation: mailpro.org/inquiries
15 minutes with our team to discuss your campaign and get expert recommendations.
Still Researching?
These resources might help:
USPS Business Mail 101 (pe.usps.com/businessmail101) — Official postal requirements
USPS Postage Calculator (postcalc.usps.com/business) — Calculate exact postage for your specs
Or just call us. We answer questions all day—even if you're not ready to order yet.
Mail Processing Associates
430 North Wabash Avenue
Lakeland, FL 33815
(863) 687-6945
orders@mailpro.org
Veteran-owned business serving clients nationwide since 1989.
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