Greeting Card Envelope Sizes: The Complete US Guide

The envelope is the first thing someone holds. Before they read the card, before they see the design, they are holding the envelope. Getting the size wrong means a bent card, a torn corner, or a piece that comes back stamped "return to sender" because it triggered a USPS non-machinable surcharge nobody knew about. This guide covers every standard greeting card envelope size, which card fits in which envelope, how postage works for each format, and the specific mistakes that cost mailers money every year.

The one rule that applies to every greeting card envelope

Choose an envelope that is 1/8 to 1/4 inch larger than your card in both height and width. This clearance lets the card slide in and out cleanly without bending the edges, and keeps the envelope from looking sloppy because there is too much empty space inside. A 5 x 7 inch card needs an envelope that is at minimum 5.125 x 7.125 inches. The A7 envelope at 5.25 x 7.25 inches is exactly right.

That 1/8 inch minimum is not a suggestion. It is the practical minimum for flat insertion. Cards that are forced into a tight envelope buckle at the corners. When the envelope goes through USPS processing, a buckled card inside creates a lumpy mailpiece that machine sensors flag as non-uniform. That can push a standard letter into non-machinable territory, adding a 49-cent surcharge per piece. On 200 wedding invitations, that is $98 in unexpected postage.

Every standard greeting card envelope size explained

A2 envelopes (4 3/8 x 5 3/4 inches)

The smallest standard card envelope in regular use. Fits cards up to 4.25 x 5.5 inches. Used for RSVP cards, small thank-you notes, gift enclosures, birthday cards on the smaller side, and personal correspondence. At 4.375 x 5.75 inches, the A2 falls well within USPS letter-size dimensions. One First-Class Forever stamp covers a standard single-card A2 mailing at one ounce. If you enclose a folded insert with the card, weigh the sealed envelope before assuming one stamp is sufficient.

A6 envelopes (4 3/4 x 6 1/2 inches)

The go-to size for 4 x 6 photo cards, modern invitations, and holiday cards. Fits cards up to 4.5 x 6.25 inches. This is also the correct size for standard 4 x 6 prints when you want to send a photo by mail without folding it. The A6 envelope at 4.75 x 6.5 inches mails at First-Class letter rate and sits comfortably within USPS dimensional limits. One Forever stamp covers it at one ounce. Most single holiday photo cards in an A6 envelope with no inserts weigh under one ounce.

A7 envelopes (5 1/4 x 7 1/4 inches)

The most widely used invitation envelope in the US. Fits cards up to 5 x 7 inches. Wedding invitations, birthday invitations, graduation announcements, formal event invitations, and 5 x 7 holiday cards all use A7. The A7 at 5.25 x 7.25 inches is the sweet spot between large enough to make an impression and small enough to mail at First-Class letter rate. One Forever stamp covers a basic suite at one ounce. A full wedding invitation suite with an inner card, RSVP card, and return envelope routinely weighs two ounces or more. Weigh a complete assembled, sealed sample before ordering your stamps.

A9 envelopes (5 3/4 x 8 3/4 inches)

The larger formal envelope. Fits cards up to 5.5 x 8.5 inches. Used for oversized announcements, formal programs, large event invitations, and anything that needs a presence that a standard A7 cannot provide. The A9 at 5.75 x 8.75 inches still mails at First-Class letter rate. One stamp covers it at one ounce. Anything over one ounce adds the standard 29-cent additional ounce rate.

Complete card-to-envelope size matching chart

Card size	Correct envelope	Envelope dimensions	Postage rate
4.25 x 5.5 in	A2	4.375 x 5.75 in	First-Class letter
4 x 6 in (photo)	A6	4.75 x 6.5 in	First-Class letter
4.5 x 6.25 in	A6	4.75 x 6.5 in	First-Class letter
5 x 7 in	A7	5.25 x 7.25 in	First-Class letter
5.5 x 8.5 in	A9	5.75 x 8.75 in	First-Class letter

 

What to use for colored greeting card envelopes

Color is a functional choice for greeting cards and invitations, not just an aesthetic one. A white envelope in a pile of white envelopes disappears. A colored envelope gets picked up first. For birthday cards, holiday mailings, event invitations, and any correspondence where the recipient's first impression matters before they even open the piece, colored envelopes do work that plain white cannot.

Business Envelopes carries colored envelopes in two formats: wove and starburst.

Wove colored envelopes are solid-color dyed stock. The color runs through the material. Professional, clean, available in multiple tones. Best for organizational correspondence where the color reinforces brand identity without being visually aggressive. Custom logo and return address printing is available on wove stock.

Starburst envelopes carry a bold multicolor pattern across the face. Designed for mailings where standing out in a pile of white is the entire objective. Used by nonprofits for fundraiser appeals, by event organizers for high-impact invitation mailings, and by direct mail programs where envelope open rate is a tracked metric. All starburst envelopes use peel-and-seal closure for fast moisture-free sealing on volume runs.

Both formats are available in #10, #9, and #6 3/4 sizes at Business Envelopes, plus 6 x 9 and 9 x 12 for larger flat mailings.

Self seal greeting card envelopes and when to use them

For anyone mailing more than a handful of cards at a time, self seal envelopes are the practical choice. No moisture, no sponge, no licking. The adhesive strip is protected by a release liner until you peel and press. The envelope seals on contact and holds through postal handling.

For holiday card runs, event invitation mailings, birthday card batches, and any mailing where you are sealing more than twenty envelopes at once, the time saving adds up fast. Self seal is also more consistent than gum flap. A gum flap that is not properly activated comes unsealed in transit. A self seal envelope that is pressed firmly is sealed for transit.

At Business Envelopes, self seal options are available across #10, #9, #6 3/4, 6 x 9, 9 x 12, 10 x 13, and 10 x 15 formats. Custom logo and return address printing is available on all self seal styles.

What no one tells you about greeting card postage

This is the section most guides skip entirely. USPS has specific rules that affect card mailing costs, and getting them wrong is expensive.

Square envelopes cost more to mail. USPS requires that the aspect ratio of a letter (length divided by height) fall between 1.3 and 2.5. A square envelope has an aspect ratio of 1:1, which falls below 1.3. It is automatically classified as non-machinable and charged a 49-cent surcharge on top of the standard First-Class rate. A square card envelope that would otherwise cost 78 cents to mail costs $1.27. On 100 pieces, that is an extra $49. Most people discover this at the post office counter after they have already ordered and addressed all 100 envelopes.

Thick invitation suites weigh more than one stamp covers. A standard wedding suite with an outer envelope, inner envelope, invitation card, RSVP card, and pre-addressed return envelope routinely hits two ounces or more. A 4 x 6 holiday photo card in an A6 envelope is usually under one ounce. A 5 x 7 card with a vellum overlay, a belly band, and an RSVP insert is almost certainly over one ounce. Weigh a fully assembled and sealed sample before purchasing stamps for a full run. One additional ounce stamp (29 cents at current rates) is a small cost. Returning and re-mailing 200 invitations is not.

Rigid card materials can trigger non-machinable classification. Thick cardstock above a certain rigidity cannot pass through postal sorting equipment without jamming. If your card is stiff enough that it does not flex at all when lightly held from opposite corners, it may be classified as non-machinable regardless of the envelope size. This most commonly affects cards printed on heavy board stock with laminate or thick coating. The solution is to take a sample to a post office counter and ask a postal employee to assess machinability before committing to a large mailing.

Wax seals add thickness and can change your postage rate. A wax seal applied to the envelope flap creates a bump that, depending on size, may push the piece into non-machinable territory. If using wax seals on invitations, apply them and weigh a sealed sample before determining your postage. The piece may still mail at letter rate, or it may need to be hand-cancelled at the post office. Ask for hand-cancellation explicitly so your wax-sealed envelopes do not go through the machine and arrive cracked.

Vertical orientation triggers a surcharge. An envelope where the height is greater than the width (taller than it is wide) is classified as non-machinable. This catches some card senders off guard when they choose portrait-orientation envelopes that are taller than they are long. Standard A-series envelopes (A2, A6, A7, A9) are all landscape orientation and avoid this issue. Custom or non-standard envelope shapes in portrait orientation will trigger the surcharge.

Greeting card envelopes for business and organizational mailings

For nonprofits, event organizers, and businesses sending greeting cards at volume, the choice of envelope has a measurable impact on results before the card is ever opened.

Colored envelopes in wove or starburst format increase the visual presence of the mailing in a stack of plain white mail. This matters for holiday card campaigns, fundraiser cards, member appreciation mailings, and event invitations where being noticed in a household mail pile is part of the objective.

Self seal envelopes reduce labor time on anything over 20 pieces. For a holiday card run of 500, the difference between lick-and-seal and peel-and-seal is roughly 30 minutes of real time and the avoidance of a genuine unpleasantness.

Printed envelopes with a custom return address and logo add a professional presence to organizational card mailings. For nonprofits, this reinforces donor recognition of the organization's name before the piece is opened. For businesses, it keeps the mailing consistent with your brand. Custom printing ships in 7 to 10 business days from proof approval.

For cards that need to arrive in perfect condition, such as handmade cards, layered die-cut pieces, or anything with embossed elements on the card face, a 9 x 12 catalog envelope lets the card travel flat without being inserted into a snug A-series envelope. The card mails as a flat rather than a letter, at a different postage rate, but arrives without edge damage or surface marking from envelope insertion.

What makes Business Envelopes different for greeting card and invitation mailing

Business Envelopes has supplied commercial envelopes to US businesses, nonprofits, event organizers, and direct mail operations since 1997. Here is what separates this catalog from a general office supply retailer when it comes to card and invitation mailing.

Every commercial size in one place. #6 3/4, #9, #10, 6 x 9, 9 x 12, 10 x 13, and 10 x 15. White, colored wove, starburst, self seal, gum flap, peel and seal. If your mailing program uses multiple envelope types across multiple pieces, all of them ship from one supplier with one order.

Self seal in every major format. Every commercial size at Business Envelopes is available with a peel-and-seal or flip-and-stick closure. No moisture required, no pre-sealing from humidity in storage, consistent sealing on every piece in the run.

Colored envelopes with custom printing. Wove solid-color envelopes and starburst pattern envelopes are available with logo and return address printing. PDF proof before production. Artwork stays on file for reorders.

Free ground shipping with no minimums. A single box of envelopes ships free to the contiguous 48 states. A pallet of mixed sizes ships free. There is no threshold to meet and no code to apply.

No minimum order quantity. Order exactly what your mailing needs. One box, five boxes, or a full case. Bulk pricing applies automatically as quantities increase, reducing the per-unit cost without requiring a minimum commitment.

The bottom line on greeting card envelopes

Card size first, envelope second. Measure your card, add 1/8 to 1/4 inch in each dimension, match to the nearest standard A-series size. Weigh a fully assembled sealed sample before purchasing stamps for any mailing over 10 pieces. Never assume a square envelope mails at the same rate as a rectangular one. Never assume a multi-insert suite weighs one ounce because the card alone does.

The envelope is not packaging. It is the first impression. A well-fitted envelope in the right color, sealed cleanly and addressed correctly, tells the recipient something about the care behind the card before they ever open it.

Frequently asked questions 

What size envelope fits a 5 x 7 greeting card?

An A7 envelope (5.25 x 7.25 inches) is the correct match. It provides 1/4 inch of clearance in each dimension, which is enough for clean insertion without excess space that makes the card shift in transit.

What size envelope fits a 4 x 6 card or photo?

An A6 envelope (4.75 x 6.5 inches). It holds a 4 x 6 print or card flat without folding and mails at First-Class letter rate with one Forever stamp at one ounce.

What size envelope fits a standard greeting card?

Most greeting cards sold at retail are either A2 size (fits a 4.375 x 5.75 inch envelope) or A7 size (fits a 5.25 x 7.25 inch envelope). Check your card's dimensions: match the longer side to the envelope's length and the shorter side to the envelope's width, with 1/8 to 1/4 inch clearance on each.

Do square envelopes cost more to mail?

Yes. Square envelopes have an aspect ratio of 1:1, which falls below the USPS minimum of 1.3. They are classified as non-machinable and charged a 49-cent surcharge on top of standard First-Class postage. A square envelope costs $1.27 to mail instead of 78 cents.

How much does it cost to mail a greeting card in 2025?

A standard rectangular card in an A2, A6, A7, or A9 envelope weighing one ounce costs 78 cents (one First-Class Forever stamp) as of July 2025. Cards over one ounce add 29 cents per additional ounce. Square or non-machinable formats cost $1.27.

Can I mail a greeting card without an envelope?

A postcard (a single piece of cardstock meeting USPS postcard dimensions: 3.5 to 4.25 inches tall and 5 to 6 inches long, no thicker than 0.016 inches) can be mailed without an envelope at the postcard rate of 61 cents. A standard greeting card is too large for postcard rate and needs an envelope.

What envelope should I use for wedding invitations?

A7 envelopes (5.25 x 7.25 inches) for standard 5 x 7 invitations. A9 envelopes (5.75 x 8.75 inches) for larger formal suites. If your suite includes multiple inserts, weigh a fully assembled sealed sample before purchasing stamps.

Do wax seals on envelopes affect postage?

Potentially yes. A wax seal adds a raised bump to the envelope flap. If that bump creates non-uniform thickness, the piece may be classified as non-machinable and charged the 49-cent surcharge. Assemble a complete sample with the wax seal applied, weigh it, and take it to a post office counter to check machinability before committing to a full run. Request hand-cancellation if you want to preserve the wax seal on delivery.

What is the difference between self seal and gum flap envelopes?

Gum flap envelopes require moisture to activate the adhesive on the flap. Self seal envelopes use a pressure-sensitive adhesive strip protected by a release liner. Peel the liner, press the flap, and the envelope is sealed. No moisture, no sponge, consistent seal on every piece. For card mailings over 20 pieces, self seal is the practical choice.