USPS rates effective April 26, 2026 (verified June 10, 2026) — source: USPS Notice 123.
How much is postage for a postcard vs. a card in an envelope?
Postcards mail for $0.61 with a postcard stamp. The moment a card goes in an envelope it mails as a letter: $0.78 for the first ounce, which is exactly one Forever stamp. The envelope — not the card inside — is what moves you between the two rates.
The postcard rate only applies to cards USPS considers postcards: between 3.5x5 and 4.25x6 inches, on paper stock thin enough to flex through the sorting machines. A 5x7 flat card is bigger than that even without an envelope, so it pays the letter rate either way.
That makes the postcard the cheapest physical card you can send — no envelope to buy, no envelope to address, and $0.17 less postage per card than an enveloped note.
When does a card need extra postage?
Add postage when a card weighs more than one ounce, can't bend, is square, or has lumps — wax seals, ribbon, charms, anything a sorting machine would jam on. Each extra ounce adds $0.29, and anything nonmachinable adds a $0.49 surcharge on top of the letter rate.
Weight is the common trap. A single card in its envelope sits well under an ounce, but heavy cardstock plus a photo insert, a folded note, or a second enclosure can tip the second ounce — $1.07 instead of $0.78. Roughly four to five sheets of regular paper weigh an ounce, so one extra enclosure is usually fine.
Texture is the sneaky one: a wax seal or ribbon makes an envelope nonmachinable even when it weighs almost nothing. If you're unsure, have the post office weigh one finished card before you stamp the whole batch.
How many stamps does a square envelope need?
A square envelope costs $1.27 to mail: the $0.78 letter rate plus the $0.49 nonmachinable surcharge. Two Forever stamps cover it but overpay $0.29 per card; USPS sells a nonmachinable-rate stamp worth exactly $1.27 for square mail.
The surcharge exists because USPS's automated sorters need a rectangle that is longer than it is tall to find and orient the address. A square envelope gets kicked out of the machine and processed by hand, and the $0.49 covers that manual handling. Rigid and unbendable envelopes ride the same rule.
On a handful of cards the two-Forever-stamps shortcut costs pennies. On fifty square invitations it wastes $14.50 — enough to be worth a trip to the counter for exact-rate stamps.
How do Forever stamps work?
A Forever stamp is always worth the current 1 oz letter rate — $0.78 today — no matter what you paid for it. Stamps bought years ago at lower prices still mail a full ounce, they never expire, and one covers a standard card in an envelope exactly.
The catch is everything that isn't a plain 1 oz letter. Forever stamps only come in one value, so covering odd rates with them always overshoots. For exact postage USPS sells companion stamps: Additional Ounce ($0.29) for heavy cards, postcard stamps ($0.61) for postcards, and a nonmachinable-rate stamp ($1.27) for square envelopes.
Stamp and postage FAQ
How many stamps do I need for a 5x7 card?
One. A 5x7 card in its A7 envelope weighs well under an ounce, so it mails at the $0.78 letter rate — exactly one Forever stamp. Only add postage if the envelope is square or rigid ($0.49 surcharge) or stuffed past one ounce ($0.29 per extra ounce).
How many stamps does a wedding invitation need?
Usually two Forever stamps — or one exact-rate stamp. Invitations with inner envelopes, RSVP cards, and heavy cardstock often weigh into the second ounce ($1.07), and square ones cost $1.27. Weigh one fully assembled invitation at the post office before stamping the whole pile.
Can I just use two Forever stamps instead of exact postage?
Yes — USPS always accepts extra postage, it just never refunds the difference. Two Forever stamps overpay a square envelope by $0.29 and a 2 oz card by $0.49. On a big batch that adds up; exact-rate stamps fix it.
Do Forever stamps expire?
No. A Forever stamp bought at any time covers the current 1 oz letter rate forever — that is the product. Old Forever stamps from years ago still mail a standard card today with nothing added; only denomination stamps (printed with a fixed cents value) can fall behind the rate.
How much does it cost to mail 100 thank-you cards?
$78.00 in stamps for standard 5x7 cards, or $61.00 for postcards — before envelopes, cards, and the hours of addressing. A print-and-mail service like ShipNote runs $1.99 per card on orders of 10+ with printing, postage, and mailing included.
What does each card format cost to mail?
All four formats side by side — postage, stamps, and what stamps-only wastes:
| Format | Postage per card | Forever stamps | Overpay with stamps only | Exact-postage option |
|---|---|---|---|---|
| Postcard (4x6, no envelope) | $0.61 | 1 | $0.17 | One postcard stamp |
| Standard card (5x7, A7 envelope, under 1 oz) | $0.78 | 1 | — | One Forever stamp |
| Square or rigid envelope | $1.27 | 2 | $0.29 | Nonmachinable-rate stamp |
| Heavy card (over 1 oz, up to 2 oz) | $1.07 | 2 | $0.49 | Forever + Additional Ounce stamp |
Done counting stamps?
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