Square envelope postage: how many stamps, the $0.49 nonmachinable surcharge, and how to avoid it

Why do square envelopes need extra postage?

USPS sorts letters on high-speed machines built for rectangles. Domestic Mail Manual (DMM) section 101.1.2 says a letter is nonmachinable when its length divided by its height is less than 1.3 or more than 2.5. A square envelope measures the same in both directions, so its ratio is 1.0, well under 1.3, and it has to be handled outside the letter machines.

That extra handling is what the nonmachinable surcharge pays for. USPS Notice 123 says letters with one or more of the DMM 101.1.2 characteristics “are subject to the $0.49 nonmachinable surcharge,” added on top of the normal price for the letter’s weight. The square card weighs the same and travels the same First-Class Mail service; it simply costs more to process.

So yes, square envelopes need extra postage, and the answer doesn’t change for a holiday card, a wedding invitation, or a thank-you note. USPS’s own letter-mailing page says it plainly: “You’ll also have to pay more if your envelopes are square or vertical (taller than they are wide).”

How much postage does a square envelope need?

Add $0.49 to the letter price for the envelope’s weight. Letter postage steps up by ounce and each price covers mail “not over” that weight, so a square card that weighs 1.1 ounces pays the 2-ounce price, not the 1-ounce price. One Forever stamp is never enough for a square envelope, even a very light one.

The prices below are USPS retail prices for stamped letters, effective July 12, 2026, and unchanged in the Notice 123 price list effective October 4, 2026. They apply to square envelopes up to 6⅛ × 6⅛ inches and no more than 1/4 inch thick.

• USPS Notice 123 price list
• How much it costs to mail a letter

How many stamps for a square envelope?

Two Forever stamps for a typical square greeting card. A card and envelope up to 1 ounce needs $1.31, and two Forever stamps add up to $1.64, which also covers a square card up to 2 ounces ($1.60). At 3 ounces ($1.89) you need a third Forever stamp. You overpay a little, but you only need one kind of stamp.

To pay the exact amount, use a nonmachinable stamp. DMM 604.1.1 lists nondenominated stamps for the “FCM non-machinable surcharge price,” and USPS’s Colorado Hairstreak butterfly stamp is one of them: the USPS stamp catalog describes it as a stamp “for use on irregularly sized envelopes, such as square greeting cards” that is “always valid for the current applicable rate printed on them.” Its pane of 20 is listed at $26.20, or $1.31 a stamp. Designs sell out, so ask at the counter or check the Postal Store before you count on one.

Any mix of stamps that adds up to the total also works; USPS says so on its letter-mailing page. A Forever stamp ($0.82), one additional-ounce stamp ($0.29), and two 10-cent stamps make exactly $1.31.

• 1-ounce square card: 2 Forever stamps, or 1 nonmachinable stamp.
• 2-ounce square card: 2 Forever stamps, or 1 nonmachinable stamp plus 1 additional-ounce stamp.
• 3-ounce square card: 3 Forever stamps, or 1 nonmachinable stamp plus 2 additional-ounce stamps.
• Not sure of the weight: weigh the sealed envelope on a kitchen or postal scale before you choose.

Can I use a Global Forever stamp on a square envelope?

Yes. DMM 604.1.1 values a Global Forever stamp at the current First-Class Mail International 1-ounce letter price, which Notice 123 lists as $1.75, and DMM 604.1.2 only requires the stamps on a piece to add up to at least the postage owed. One Global Forever stamp therefore covers a domestic square card up to 2 ounces ($1.31 or $1.60). You overpay by 44 cents or 15 cents, so it makes sense mainly when the Global Forever stamp is the one you already have.

Two Forever stamps are the cheaper everyday choice. One Forever stamp plus a postcard stamp ($0.82 + $0.65 = $1.47) also covers a 1-ounce square card.

What is the nonmachinable surcharge in 2026?

The nonmachinable surcharge is $0.49 per retail First-Class Mail letter. It is part of the USPS retail prices effective July 12, 2026, and the Notice 123 price list effective October 4, 2026 keeps it at $0.49. It is a single flat amount: a 1-ounce and a 3.5-ounce nonmachinable letter both pay $0.49 on top of their letter price.

The surcharge applies to letter-size mail only, up to 3.5 ounces. Postcard-size pieces are excluded by DMM 101.6.3.1, which applies the surcharge to “letter-size pieces (except card-size pieces).” Large envelopes don’t pay it either; a large envelope that is rigid, not rectangular, or not evenly thick pays package prices instead, which Notice 123 starts at $8.40 for USPS Ground Advantage retail.

Mail to other countries has the same charge. Notice 123 lists a $0.49 nonmachinable letter surcharge for First-Class Mail International, so a 1-ounce square card to Canada, Mexico, or any other country costs $1.75 + $0.49 = $2.24. International letters must also be at least 5½ inches long, so a 5 × 5 square can’t go abroad at letter prices at all.

What makes a letter nonmachinable?

Square is the most common reason, but it isn’t the only one. DMM 101.1.2 lists every characteristic, and one is enough to add the $0.49 surcharge. Measure the envelope with the address facing you: the length is the side parallel to the address, and the height is the side perpendicular to it (DMM 601.1.1.2).

• Its aspect ratio, length divided by height, is less than 1.3 or more than 2.5. That covers square envelopes and near-square ones, such as a 5 × 6 card (1.2).
• It is polybagged, wrapped in plastic, or its outside isn’t paper. Paper envelopes with windows are fine.
• It has clasps, strings, buttons, or similar closures, including ribbon ties.
• It contains pens, pencils, keys, coins, or similar items that make it unevenly thick, or loose objects that can slide around inside.
• It is too rigid to bend easily; USPS tests this as bending around an 11-inch-diameter turn at 40 pounds of belt tension.
• It is thinner than 0.009 inch while longer than 6 inches or taller than 4¼ inches.
• The delivery address runs parallel to the shorter side, as on a card addressed vertically.
• It is a self-mailer or booklet that isn’t prepared to USPS’s standards for those formats.

• DMM 101: Physical standards (section 1.2, nonmachinable criteria)

Do wax seals, ribbons, and thick invitations need extra postage?

Usually, yes. The DMM list doesn’t name wax seals, but a seal raises one spot of the envelope, which is the uneven thickness the rule describes, and a stiff layered invitation can fail the rigidity test. Ribbons and string ties are named outright as closure devices. Plan on the $0.49 surcharge for any of them, or have a retail associate measure one at the counter before you stamp the whole batch.

USPS’s advice for embellished invitations has two parts. You can pay the nonmachinable price, bring the envelopes to the Post Office counter, and ask for them to be hand-canceled. For decorations on the outside, such as wax seals, strings, or ribbons, USPS says not to send them exposed and to put them inside another envelope instead.

An outer envelope protects the decoration, but it doesn’t automatically make the piece machinable. If the seal still makes the outer envelope lumpy or the stack is too stiff to bend, the surcharge still applies.

• USPS: How to send a letter or postcard (embellished invitations)

Square envelope sizes and their postage

Size decides which price table a square card uses. A letter can be up to 6⅛ inches high, so squares up to 6⅛ × 6⅛ inches are nonmachinable letters, as long as they meet the other letter limits. Anything larger on a side is a large envelope (USPS calls it a flat), which pays flat prices and no nonmachinable surcharge, as long as it bends and is evenly thick. Squares smaller than 5 inches on a side are under the 5-inch minimum length for a letter and aren’t mailable on their own (DMM 601.1.1.3).

The table assumes a flexible envelope no more than 1/4 inch thick for letters, and no more than 3/4 inch thick for flats, at USPS retail prices effective July 12, 2026 and unchanged on October 4, 2026.

• Envelope sizes and which ones mail as letters
• DMM 601: Mailability (length, height, and address placement)

How to check whether an envelope is machinable

Divide the length by the height. If the answer is from 1.3 to 2.5 (both ends count, per DMM 601.1.1.3), the shape passes. Most standard rectangular envelopes pass easily; the ones that fail are squares and some boutique sizes that are close to square. Then check the rest of the list: flexible, evenly thick, no clasp or ribbon, address running along the long side.

Does a vertical address make a card nonmachinable?

Yes. USPS measures a letter’s length along the address, so turning a rectangular card on end and addressing it top to bottom changes the math. DMM 101.1.2 lists a delivery address parallel to the shorter side as a nonmachinable characteristic, and DMM 601.1.1.3 adds that a letter whose side parallel to the address is under 5 inches isn’t mailable at all.

DMM 601’s own example is a 4 × 6 piece: addressed along the 4-inch side, it is only 4 inches long and is nonmailable. Write the address in the center of the long side, the way the envelope sits when it is wider than tall, and a standard card stays at the $0.82 letter price.

• How to address Christmas cards

What happens if you mail a square envelope with one stamp?

It comes back to you. Ordinary shortpaid mail can be delivered with postage due, but DMM 604.8.1.1 excludes nonmachinable First-Class Mail from that rule, and DMM 604.8.1.3 says “shortpaid nonmachinable First-Class Mail letters are returned to the sender for additional postage.” Your recipient doesn’t get the card and doesn’t get a bill for it.

The stamp you already used isn’t wasted. Under DMM 604.8.1.4, postage already on a returned piece counts at face value when you mail it again, so add the missing amount (one more Forever stamp, or 49 cents in smaller stamps for a 1-ounce card) and send it back out.

A return address matters here. DMM 604.8.1.2 treats insufficient-postage mail with no return address as dead mail, so a square card without one may never reach anyone. During the holidays, a returned card also loses days, so stamp it correctly the first time if it has to arrive before December 25; USPS recommends mailing First-Class Mail by Thursday, December 17, 2026.

• DMM 604.8: Insufficient or omitted postage
• Returned to sender: what it means

How to avoid the nonmachinable surcharge

The surcharge is about shape and construction, so the fix is in the envelope, not the stamp. If you are choosing cards for a long list, the savings add up: 50 square cards at $1.31 cost $65.50 in postage, while the same cards in rectangular envelopes at $0.82 cost $41.00.

• Pick a rectangular envelope with a ratio between 1.3 and 2.5. An A7 envelope fits a 5 × 7 card at the $0.82 letter price.
• Keep the outside flat and paper: no wax seal, ribbon, button, or clasp on the envelope itself.
• Leave rigid add-ons out of letter mail. Thick chipboard, coins, or keys belong in a padded envelope or small box sent as a package.
• Address it along the long side, not vertically.
• Send a postcard instead. A rectangular card from 3½ × 5 to 4¼ × 6 inches mails with one $0.65 postcard stamp.
• Let a print-and-mail service handle postage. An IRIS postcard is rectangular and its First-Class postage is part of the price.

• How much is a postcard stamp?

Sending a holiday card without stamps

IRIS prints and mails personal postcards by USPS First-Class Mail to US addresses. You choose a holiday design or upload your own photo, type the message, enter the recipient’s address, and see the total before you pay. A 4 × 6 or 5.5 × 4.25 postcard costs $3.49 and a 6 × 9 or 8.5 × 5.5 postcard costs $4.49, with full-color printing and postage included, so there is no square-envelope math and no stamp to buy.

For a longer note, IRIS mails letters too: upload a US Letter-size PDF and a one-page black-and-white letter costs $3.20 with First-Class postage included. Each order goes to one recipient, the message is printed rather than handwritten, and IRIS can’t enclose a physical card, so if your heart is set on a particular square card, stamp it yourself using the table above.

• Holiday postcards
• Send a letter online