Short answer: a standard one-ounce letter needs one Forever stamp ($0.82 in 2026). A postcard needs one postcard stamp ($0.65), and a one-ounce letter going anywhere internationally needs one Global Forever stamp ($1.75). Heavier or larger items need more, and this guide gives you the exact count for every common piece of mail, plus the fastest way to skip the math entirely.
The number of stamps comes down to three things: the size of what you are sending (letter, postcard, or large envelope), how much it weighs, and where it is going. Get those three right and the postage falls into place. Here is the full breakdown at current USPS rates.
How many stamps do I need? Quick reference
For the most common items, this is all most people need:
| What you are mailing | Postage (2026) | Simplest stamps |
|---|---|---|
| Standard letter, 1 oz | $0.82 | 1 Forever stamp |
| Standard letter, 2 oz | $1.11 | 2 Forever stamps |
| Postcard | $0.65 | 1 postcard stamp |
| Large envelope (9×12), 1 oz | $1.69 | 3 Forever stamps |
| International letter, 1 oz | $1.75 | 1 Global Forever stamp |
Those cover the vast majority of everyday mail. Below, each one is broken down by weight so you never over- or under-pay. If you would rather not count at all, our free Stamp Calculator tells you the exact postage and how many Forever stamps to use for any weight in a couple of seconds.
How many stamps for a standard letter?
A standard First-Class letter, the kind that fits in a normal business or greeting-card envelope, starts at $0.82 for the first ounce, which is exactly one Forever stamp. Every additional ounce adds $0.29, up to the 3.5-ounce limit where letter rates stop and large-envelope rates begin.
| Letter weight | Postage | Exact postage | Forever stamps only |
|---|---|---|---|
| Up to 1 oz | $0.82 | 1 Forever | 1 |
| Up to 2 oz | $1.11 | 1 Forever + one 29¢ stamp | 2 (overpays $0.53) |
| Up to 3 oz | $1.40 | 1 Forever + two 29¢ stamps | 2 (overpays $0.24) |
| Up to 3.5 oz | $1.69 | 2 Forever + one 5¢ stamp | 3 (overpays $0.77) |
The takeaway: if you only have Forever stamps on hand, two of them cover any letter up to 3 ounces, you just overpay a little. To pay the exact amount, keep a few one-ounce additional-rate stamps (currently 29¢) in the drawer. Anything heavier than 3.5 ounces is no longer a letter in USPS’s eyes; it jumps to large-envelope pricing, covered below.
The two-ounce question: wedding invitations and heavy cards
This is the single most common stamp mistake, so it earns its own section. A wedding invitation with an RSVP card, an inner envelope, or thick cardstock almost always tips over one ounce into the two-ounce tier at $1.11. People put a single Forever stamp on it, and the whole batch comes back marked postage due, sometimes after the RSVP date has passed.
If you are mailing invitations or chunky greeting cards, weigh one fully assembled piece first. If it is over an ounce, use two Forever stamps each (or a Forever plus a 29¢ stamp to pay exactly). And if your envelopes are square, which many invitations are, keep reading, because square envelopes trigger an extra surcharge on top of the weight.
How many stamps for a large envelope (manila / 9×12)?
Once you move up to a large envelope, often called a flat, such as a 9×12 manila envelope holding unfolded documents, the rate changes. Large envelopes start at $1.69 for the first ounce and add $0.29 per additional ounce, all the way up to 13 ounces.
| Large envelope weight | Postage | Forever stamps |
|---|---|---|
| Up to 1 oz | $1.69 | About 3 (or 2 + a 5¢ stamp) |
| Up to 2 oz | $1.98 | About 3 |
| Up to 4 oz | $2.56 | About 4 |
| Up to 8 oz | $3.72 | About 5 |
Because Forever stamps are worth $0.82 each toward any of these, covering a flat with them alone always overpays a bit. For anything over about 10 ounces, or for anything with real thickness or bulk, you are usually better off shipping it as a package with USPS Ground Advantage rather than piling on stamps. Our Postage Price Calculator shows the package price so you can compare, and for boxes the Flat Rate Box Selector often beats weight-based pricing. If you are mailing a bigger parcel, our guide to what it costs to ship a package with USPS lays out every option.
How many stamps for a postcard?
A standard postcard needs just one postcard stamp at $0.65, which is cheaper than a letter. You can use a regular Forever stamp on a postcard, but you would be overpaying by $0.17 every time, so buy actual postcard stamps if you send them often.
One catch: the discounted postcard rate only applies to cards within the standard size range, roughly 3.5 by 5 inches up to 4.25 by 6 inches. An oversized card larger than that is billed as a letter and needs a full Forever stamp or more, depending on weight.
How many stamps for international mail?
To send a one-ounce letter or a postcard to any other country, you need one Global Forever stamp, which costs $1.75 and works to every international destination at the one-ounce letter rate. Like the domestic Forever stamp, it holds its value even when rates rise, so it is the simplest way to send mail abroad.
Heavier international letters cost more, and the exact price depends on the destination country’s price group, so once you are over an ounce it is worth checking the precise amount rather than guessing. Our Stamp Calculator handles international letters too, and you should always confirm what the destination country prohibits before sending anything of value.
When you need extra postage: non-machinable mail
USPS sorts most letters on automated equipment, and anything that cannot run through that equipment gets a non-machinable surcharge on top of the normal postage. Your letter is non-machinable if it is:
- Square (very common for wedding and party invitations)
- Rigid or unable to bend, or lumpy and uneven
- Sealed with a clasp, string, or button
- Unusually tall relative to its width
The surcharge is a fixed extra fee added to the weight-based postage, which is why a square invitation costs more than a rectangular one of the same weight. If your envelope fits any of the above, add postage beyond the base rate. The Stamp Calculator factors the surcharge in automatically so you are not guessing.
Forever stamps: why they are the smart default
A Forever stamp is always worth the current First-Class one-ounce rate, no matter when you bought it. Buy one today at $0.82 and it will still mail a one-ounce letter years from now, even after the price rises. That makes stamps one of the few things that quietly beat inflation, so if you mail regularly it is worth stocking up rather than buying one book at a time. And if you have found old stamps in a drawer and are wondering whether they still work, the good news is they almost certainly do, which we cover in do postage stamps expire. For how stamps are sold and how many come in a book, see how many stamps in a book.
A quick note on weighing your mail
Almost every stamp mistake traces back to a wrong weight guess. A single sheet of paper in an envelope is well under an ounce, but a few sheets, a card, and a thick envelope add up faster than people expect. A cheap kitchen or postal scale pays for itself the first time it saves you a postage-due return. If you do not have a scale handy, our guide on how many sheets of paper per stamp gives you a reliable rule of thumb for ordinary letters.
Where to buy stamps
You can buy stamps at the Post Office counter, from USPS.com, at self-service kiosks, and at many everyday retailers, grocery stores, pharmacies, and big-box chains all sell books of Forever stamps near the checkout or customer service desk. If you are wondering whether a specific chain carries them, our guide on whether CVS sells stamps is a good example of what to expect at a drugstore. Buying online or at a retailer is usually the most convenient, and you avoid the Post Office line entirely.
The easiest way: let the calculator do it
All of the above is useful to understand, but you do not have to memorize any of it. Enter the type of mail, its weight, and the destination into our free Stamp Calculator, and it returns the exact postage and the simplest stamp combination, surcharges included. For packages, the Postage Price Calculator does the same with live-style USPS pricing. Between the two, you will never guess at postage again.
Frequently asked questions
How many stamps do I need for a normal letter?
One Forever stamp ($0.82 in 2026) covers a standard letter up to one ounce. If it weighs more, add a 29¢ stamp per additional ounce, or use two Forever stamps to cover any letter up to three ounces.
How many stamps for a 2 oz letter?
A two-ounce letter costs $1.11, which is one Forever stamp plus one 29¢ additional-ounce stamp, or simply two Forever stamps if you do not mind overpaying by about 53 cents. This is the tier most wedding invitations fall into.
How many stamps for a 9×12 envelope?
A large 9×12 envelope starts at $1.69 for the first ounce, which is about three Forever stamps, plus 29¢ for each additional ounce. Over roughly 10 ounces, shipping it as a package is usually cheaper.
How many stamps do I need to mail a letter internationally?
One Global Forever stamp, which costs $1.75, mails a one-ounce letter or a postcard to any country. Heavier international letters cost more depending on the destination country’s price group.
Can I use two Forever stamps instead of exact postage?
Yes. USPS accepts extra postage, so two Forever stamps will safely cover any letter up to three ounces. You simply pay a little more than the exact rate. You cannot pay less, though, or the mail comes back postage due.
Do I need extra postage for a square envelope?
Yes. Square envelopes are non-machinable and carry a fixed surcharge on top of the normal letter postage, even if they weigh under an ounce. Budget for more than a single Forever stamp on invitations.
The bottom line
For everyday mail it is simple: one Forever stamp for a standard letter, one postcard stamp for a postcard, and one Global Forever stamp for international. The count only climbs when the weight, size, or shape changes, and the two things that trip people up most are heavier two-ounce invitations and non-machinable square envelopes. When in doubt, weigh the piece and run it through the Stamp Calculator, and you will get it right the first time, every time.