Envelope Sizes and Types Explained: What to Use, When to Use It, and What You Can Print

Choosing the right envelope isn’t just about size—it affects postage costs, USPS automation, deliverability, branding, and customer response rates. As a presort mailing and full‑service printing company, we help businesses select envelopes that mail efficiently and present their brand professionally. 

This guide explains the most common envelope sizes and types, what they’re best used for, and what can be printed on them for compliant, cost‑effective mailing. 

Why Envelope Selection Matters in Presort Mailing 

The envelope you choose can directly impact: 

• USPS automation eligibility 

• Postage discounts through presort 

• Address readability and barcode placement 

• Brand appearance and open rates 

Using the wrong envelope can increase postage, cause processing delays, or even result in returned mail. 

Common Envelope Sizes and Their Best Uses 

#10 Envelope (4.125" x 9.5") 

Best for: 

• Business letters 

• Invoices and statements 

• Notices and transactional mail 

Why it’s popular: The #10 envelope is the most widely used commercial envelope and is fully compatible with USPS automation and presort discounts. 

What can be printed: 

• Return address or company logo 

• Recipient address (with OCR‑friendly fonts) 

• Intelligent Mail Barcode (IMb) 

• Marketing messages or teaser copy 

• Windowed or non‑windowed layouts 

✅ Presort‑friendly and cost‑effective 

#9 Envelope (3.875" x 8.875") 

Best for: 

• Reply envelopes mailed inside a #10 

• Business reply mail (BRM) 

What can be printed: 

• Preprinted return address 

• USPS Business Reply indicia 

• Tracking barcodes 

📬 Often paired with statements, donation appeals, and customer responses. 

A7 Envelope (5.25" x 7.25") 

Best for: 

• Invitations and announcements 

• Reminder cards 

• Thank‑you notes 

What can be printed: 

• Full‑color graphics 

• Logos and branding 

• Recipient addresses (may require hand‑sorting if not automation‑compliant) 

⚠️ Note: Some A7 sizes may not qualify for automated USPS processing, impacting postage costs. 

A2 Envelope (4.375" x 5.75") 

Best for: 

• Greeting cards 

• Small promotional mailings 

• Event announcements 

What can be printed: 

• Decorative designs 

• Addresses and branding 

These are often hand‑sorted and best for targeted or specialty campaigns. 

#6¾ Envelope (3.625" x 6.5") 

Best for: 

• Personal correspondence 

• Checks and compact inserts 

What can be printed: 

• Return address 

• Recipient address 

Less commonly used in high‑volume presort mail but still useful for niche applications. 

Flat Envelopes: Large-Format Mailing Options 

Flat envelopes are considered “flats” by USPS, offering more space but higher postage. 

6" x 9" Flat Envelope 

Best for: 

• Booklets 

• Folded brochures 

• Legal documents 

What can be printed: 

• Addresses 

• Barcodes 

• Full‑bleed designs 

Often used for marketing inserts where presentation matters. 

9" x 12" Flat Envelope 

Best for: 

• Reports 

• Contracts 

• Certificates 

• Forms that should not be folded 

What can be printed: 

• Branding and logos 

• Address blocks 

• Tracking barcodes 

📦 These typically mail at flat rates but can still qualify for presort discounts at scale. 

Window vs. Non‑Window Envelopes 

Window Envelopes 

Best for: 

• Statements 

• Invoices 

• High‑volume transactional mail 

Advantages: 

• No need to print labels 

• Automation‑friendly 

• Reduces insertion errors 

What must align: 

• Address placement on insert 

• USPS‑approved window size and positioning 

Non‑Window Envelopes 

Best for: 

• Marketing campaigns 

• Personalized branding 

• Specialty mail 

What can be printed: 

• Variable data addresses 

• Promotional messaging 

• Personalized graphics 

Offers maximum design flexibility. 

Specialty Envelope Types 

Booklet Envelopes 

Opening on the long edge, ideal for brochures and catalogs. 

Best for: 

• Product catalogs 

• Multi‑page marketing pieces 

Catalog Envelopes 

Opening on the short edge, often used for documents and manuals. 

Best for: 

• Technical documents 

• Instructional materials 

Security Tint Envelopes 

Printed with interior patterns to prevent sensitive information from showing through. 

Best for: 

• Financial statements 

• Medical notices 

• Legal correspondence 

What Information Can Be Printed on Envelopes? 

Depending on your mailing strategy, envelopes can include: 

• Company name and logo 

• Return address 

• Recipient address 

• USPS Intelligent Mail Barcode (IMb) 

• Permit or indicia 

• QR codes or promotional URLs 

• Marketing messages or calls to action 

✅ As a presort mailer, we ensure layouts meet USPS automation and barcode clearance requirements. 

Envelope Design Tips for USPS Automation & Presort 

• Use high‑contrast text for addresses 

• Avoid script or decorative fonts in address blocks 

• Leave clear zones for barcodes 

• Choose envelope sizes that meet USPS machinable standards 

• Match envelope choice to mailing volume 

These steps help maximize postage savings and delivery speed. 

Frequently Asked Questions  

What is the most common envelope size for business mail? 

The #10 envelope is the most commonly used size for business letters, invoices, and statements. 

Can envelopes be printed with logos and marketing messages? 

Yes. Envelopes can include logos, branding, messaging, and even personalized graphics as long as USPS placement rules are followed. 

Do envelope sizes affect postage? 

Yes. Envelope size, thickness, and weight determine whether mail qualifies as a letter, flat, or parcel—each with different postage rates. 

Are window envelopes better for presort mail? 

Often, yes. Window envelopes streamline production and improve automation compatibility, especially for statements and notices. 

Work With a Presort Mailer Who Gets It Right 

From envelope selection and design to printing, inserting, presorting, and USPS delivery,

choosing the right partner makes all the difference. 

If you’d like help selecting the best envelope for your next mailing—or want to ensure your mail qualifies for the maximum USPS postage discounts—we’re here to help. 

Ready to mail smarter? Contact us today.