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A square greeting card needs more than a standard letter stamp: its shape makes it nonmachinable, so the post office adds a surcharge on top of regular postage. Square cards cannot run through sorting machines the normal way and must be handled by hand. Weigh the card and check the surcharge before mailing.
Postal sorting machines are built for rectangles. A letter moves through the machine lengthwise, and the machine reads the address while the piece travels in one orientation. A square card has no long side to lead with, so it can tumble, jam, or arrive at the reader sideways. Rather than risk a jam that damages other mail, the post office pulls square pieces out of the machine stream and sorts them by hand. The nonmachinable surcharge pays for that hand work.
The rule behind it is an aspect-ratio rule: a machinable letter must be clearly longer than it is tall, within a set ratio range. A square card, where length equals height, fails that test by definition. This is true regardless of size: a small square card and a large square card both trigger the surcharge, because the problem is the shape, not the dimensions. Odd shapes, such as round or heart-shaped cards, fail the same test and are handled the same way.
| Card type | Machinable? | Postage needed |
|---|---|---|
| Standard rectangular card | Yes, if it meets size and flexibility rules | Regular letter postage for its weight |
| Square card | No | Regular postage plus the nonmachinable surcharge |
| Square card with a rigid insert | No | Regular postage plus surcharge; may price as a larger piece if thick |
| Oversize square card | No | Surcharge, and possibly large-envelope pricing if it exceeds letter limits |
At a post office counter, the clerk weighs the card, confirms the surcharge, and prints the correct postage. That is the simplest path, especially for holiday card batches where several cards may differ in weight. If you are using stamps at home, you need enough stamp value to cover both the base postage and the surcharge: one standard stamp alone will leave a square card short. When in doubt, add the extra stamp value before dropping the card in a mailbox, because a short-paid card may come back to you or arrive with postage due.
A kitchen scale helps here. Cards with glitter, layered paper, ribbons, or photo prints weigh more than plain cards, and weight can push a card into a higher postage band on top of the surcharge. Weigh one finished card, envelope and all, before you buy stamps for the whole batch. Guessing from an unfinished card is how holiday mail ends up returned in January.
Holiday cards are where this surcharge bites most people, because square cards are popular for Christmas, Hanukkah, and New Year designs, and they are mailed in batches. A sender who buys standard stamps for fifty square cards and mails them all short will get a stack of returns, or worse, will have recipients asked to pay postage due on a greeting. Neither outcome matches the spirit of the card.
Plan the batch in advance. Finish one card completely, with its insert, photo, and envelope, weigh it, and take it to the post office to confirm the total postage. Then buy stamps in that exact value for the rest of the batch. If you order printed cards online, check the finished size before ordering: many photo-card services default to a square format, and switching to a rectangular format at order time avoids the surcharge entirely.
Canada Post also charges more for square and other non-standard shapes, under its own oversize and non-standard rules. The mechanism differs, square mail may price as a non-standard or oversize lettermail item, but the principle is the same: shapes that do not fit machine sorting cost more. If you are mailing square cards from Canada, check the current Canada Post size and shape guide before buying stamps, and expect a higher price than a standard rectangular card.
For international square cards, the surcharge stacks with international postage, so a square card to another country costs the international rate plus the nonmachinable fee. That combination surprises senders who budgeted only for the international rate. Confirm the total at the counter for the first card, then replicate it across the batch.
LetterAgent mails printed letters on standard letter paper in a double-window envelope, not greeting cards, so a square card is outside what it sends. If your message fits a standard letter, describe it to your AI assistant, approve the exact quoted price, and it is printed and mailed to a US or Canadian address. For the square cards themselves, the post office counter remains the right tool.
Ready to mail it? Send your letter with LetterAgent: describe it to your AI assistant, approve the exact quoted price, and it is printed and mailed.
LetterAgent is a working name. Prices include print, postage, and our service fee. US prices in USD, Canadian prices in CAD (Canadian prices exclude applicable sales tax, added at checkout). Currently in private testing.
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