Skim-friendly cheat sheet
| Envelope style | Typical outside size (in) | Ideal insert (in) | Best use case |
|---|---|---|---|
| #10 Business | 4 ⅛ × 9 ½ | 3 ⅞ × 9 ¼ | Invoices, letters |
| 6 × 9 Catalog | 6 × 9 | 5 ¾ × 8 ¾ | Policy mailers |
| 9 × 12 Booklet | 9 × 12 | 8 ¾ × 11 ¾ | Sales brochures |
Need something off-list? You can always ask Pakoro for a fully custom dieline that slips through automated inserters without a hiccup.
Why “standard” envelope sizes are only the beginning
You probably know that printers talk about standard sizes all the time. Yet your mailing machinery, postal rules, and brand layout rarely match those one-size-fits-all numbers. That’s why we at Pakoro treat every envelope as a custom project.
“When you tweak a flap by even 2 mm, you can boost inserting speed by 15 %.”
Ready to dial in your own specs? Jump straight to our contact form and drop us the inserts you need to protect.
Business Envelope Sizes (Direct- & Transactional-Mail Heroes)
A business envelope opens on the long side and glides through postage meters with ease. You send them every day—so shaving grams and fractions of an inch saves real money.
| Name | Outside (in) | Max insert (in) |
|---|---|---|
| 6¼ | 3 ½ × 6 | 3 ¼ × 5 ¾ |
| 6¾ | 3 ⅝ × 6 ½ | 3 ⅜ × 6 ¼ |
| 7 | 3 ¾ × 6 ¾ | 3 ½ × 6 ½ |
| 8⅝ | 3 ⅝ × 8 ⅝ | 3 ⅜ × 8 ⅜ |
| 9 | 3 ⅞ × 8 ⅞ | 3 ⅝ × 8 ⅝ |
| 10 | 4 ⅛ × 9 ½ | 3 ⅞ × 9 ¼ |
| 11 | 4 ½ × 10 ⅜ | 4 ¼ × 10 ⅛ |
| 12 | 4 ¾ × 11 | 4 ½ × 10 ¾ |
| 14 | 5 × 11 ½ | 4 ¾ × 11 ¼ |
Pro tip: Stick with the #10 when you need maximum machinability and the lowest postage tier.
Booklet Envelope Sizes (Side-Opening, Book-Friendly)
Booklet envelopes open on the long edge. That makes them perfect for brochures, contracts, or any insert you want to slide in like a paperback.
| Name | Outside (in) | Max insert (in) |
|---|---|---|
| 6 | 5 ¾ × 8 ⅞ | 5 ½ × 8 ⅝ |
| 6½ | 6 × 9 | 5 ¾ × 8 ¾ |
| 6⅝ | 6 × 9 ½ | 5 ¾ × 9 ¼ |
| 9 | 8 ¾ × 11 ½ | 8 ½ × 11 ¼ |
| 9½ | 9 × 12 | 8 ¾ × 11 ¾ |
| 10 | 9 ½ × 12 ⅝ | 9 ¼ × 12 ⅜ |
Need a thumb-cut or a peel-and-seal strip? Tell us when you brief your project. Small extras often lift open-rate and brand recall.
Catalog Envelope Sizes (End-Opening, Bulk Protectors)
When you ship policies or glossy catalogs flat, you can’t risk a side seam tearing. Catalog envelopes open on the short edge, use a center seam, and carry heavier paper stocks without warping.
| Name | Outside (in) | Max insert (in) |
|---|---|---|
| 6 × 9 | 6 × 9 | 5 ¾ × 8 ¾ |
| 9 × 12 | 9 × 12 | 8 ¾ × 11 ¾ |
| 10 × 13 | 10 × 13 | 9 ¾ × 12 ¾ |
How to choose the right envelope—fast
- Measure your insert after folds.
- Add at least ⅛ in clearance per side.
- Check postal thickness rules if you mail in bulk.
- Pick flap style: side for automation, end for strength.
- Confirm stock weight so dark inks stay opaque.
Still unsure? A two-minute chat with a Pakoro engineer can lock in the spec and the savings.
Next steps
- 📥 Download the full PDF cheat sheet on our Envelope Hub (free).
- 📞 Talk to a packaging engineer—use our quick form at pakoro.com/contact and get a dieline today.
- 💡 Ask about branded liners—even a pop of color inside the flap can raise response rates.
Because you deserve envelopes that fit first time, every time—and Pakoro is here to make that happen.
