Introduction
Square envelopes are the invitation world’s signature format — the 5×5 and 6×6 squares that carry wedding invitations, announcements, and greeting cards with a distinctive, modern feel that rectangular envelopes can’t match.
But square envelopes carry a catch: they’re non-standard for postal sorting, and most postal services apply a surcharge for square mail. This guide covers square envelope sizes, which occasions they suit, and the postage rule you need to factor in before committing.
Common Square Sizes
Square envelopes come in a few standard dimensions.
| Size | Dimensions | Typical Use |
|---|---|---|
| 5×5 | 5″ × 5″ | Small cards, RSVPs |
| 5½×5½ | 5.5″ × 5.5″ | Invitations, cards |
| 6×6 | 6″ × 6″ | Invitations, announcements |
| 6½×6½ | 6.5″ × 6.5″ | Larger invitations |
| A7 square | ~5¼” × 5¼” | Invitation suites |
In addition, the A-series offers square-adjacent formats:
| A-Size | Dimensions | Note |
|---|---|---|
| A7 | 5¼” × 7¼” | Rectangular, not square |
| A8 | 5½” × 8⅛” | Rectangular |
| Square A7 | 5¼” × 5¼” | True square variant |
To choose a square size:
| If your insert is… | Square envelope |
|---|---|
| 5×7 invitation | 5×5 (fits folded) |
| 6×6 card | 6×6 |
| RSVP card | 5×5 |
Square vs Rectangular
Square envelopes are chosen for look, but the trade-off is postage.
| Trait | Square | Rectangular |
|---|---|---|
| Look | Modern, distinctive | Traditional |
| Postage | Surcharge | Standard |
| Best for | Invitations, cards | Business mail |
The surcharge is the key difference — square pieces are non-machinable and cost more to mail than a standard #10 or A7.
| Factor | Square Detail |
|---|---|
| Machinability | Non-machinable |
| Surcharge | Applies to square mail |
| Impact | Adds cost per piece |
Square Envelopes for Invitations
Square is the invitation format of choice for a reason.
| Invitation type | Square fit |
|---|---|
| Wedding invitations | 6×6 common |
| Save-the-dates | 5×5 or 6×6 |
| Birthday / event | 5×5 |
| Baby announcements | 5½×5½ |
Square envelopes pair naturally with square cards and are a signature of modern stationery design.
| Benefit | Why it works |
|---|---|
| Distinctive | Stands out from bills |
| Modern feel | Contemporary design language |
| Card match | Pairs with square cards |
Postage Rules for Square Mail
This is the part most people miss. Square envelopes attract a non-machinable surcharge.
| Rule | Detail |
|---|---|
| Square = non-machinable | Sorted by hand |
| Surcharge | Extra fee per piece |
| Reason | Square can’t tumble in machines |
Before ordering square envelopes in bulk, factor this in:
| Step | Action |
|---|---|
| 1 | Confirm current surcharge |
| 2 | Weigh the piece |
| 3 | Budget postage + surcharge |
| 4 | Verify address placement |
If postage cost is a concern, a rectangular A7 (5¼×7¼) delivers a similar invitation feel without the square surcharge.
Use Cases
| Use case | Square envelope |
|---|---|
| Wedding suite | 6×6 outer |
| RSVP | 5×5 reply |
| Greeting cards | 5×5 |
| Holiday cards | 6×6 |
| Luxury brands | 6×6 with liner |
Two cases deserve note. Weddings favor 6×6 for a keepsake opening moment; greeting-card brands favor 5×5 for shelf presence.
Conclusion
Square envelope sizes — 5×5, 5½×5½, and 6×6 — are the invitation world’s signature, offering a modern, distinctive look that pairs with square cards. Just remember the postage rule: square mail is non-machinable and carries a surcharge, so factor that cost in before ordering in bulk. For the invitation-size picture, see our invitation envelope sizes guide; for liner pairings, our custom envelope liners piece.
Need square envelopes for your invitations? Request a quote.