For most letters, the answer is one. A standard rectangular envelope weighing 1 ounce or less needs a single Forever stamp — currently $0.82 — to travel anywhere in the United States. You only need extra postage when the letter is heavier than 1 ounce, unusually shaped, or going to another country. This page walks through each case using the current USPS prices (in effect since July 12, 2026), and is part of our Postage & Stamp Guides center.
Key Takeaways
- A standard letter up to 1 oz needs exactly one Forever stamp — $0.82 — to anywhere in the United States.
- Each additional ounce costs 29¢, up to the 3.5 oz letter maximum (2 oz $1.11, 3 oz $1.40, 3.5 oz $1.69). Use additional-ounce stamps, not a second Forever stamp.
- Square, rigid, or lumpy letters add a 49¢ nonmachinable surcharge, however light they are.
- Over 3.5 oz or beyond letter dimensions, the piece is priced as a large envelope from $1.69. A letter abroad costs $1.75.
How Many Stamps by Letter Weight
First-Class Mail letters are priced by weight in whole-ounce steps, and any fraction of an ounce rounds up to the next step. A letter that weighs 1.2 ounces pays the 2-ounce price.
| Letter weight | Total postage | A practical way to pay it |
|---|---|---|
| Up to 1 oz | $0.82 | 1 Forever stamp |
| Over 1 oz, up to 2 oz | $1.11 | 1 Forever stamp + one 29¢ additional-ounce stamp |
| Over 2 oz, up to 3 oz | $1.40 | 1 Forever stamp + two 29¢ additional-ounce stamps |
| Over 3 oz, up to 3.5 oz | $1.69 | 1 Forever stamp + three 29¢ additional-ounce stamps |
| Over 3.5 oz | From $1.69 | Priced as a large envelope (see below) |
Notice what is not on this list: a second Forever stamp. Two Forever stamps put $1.64 of postage on a 2-ounce letter that only costs $1.11 — you would be overpaying by 53 cents. Forever stamps are for the first ounce; additional-ounce stamps (sold at the current 29-cent additional-ounce price) exist precisely for the remaining weight. If you are new to how the Forever system works, start with What Is a Forever Stamp?
A typical 1-ounce letter, for reference: a standard #10 envelope with about four or five sheets of ordinary copy paper inside. One or two sheets more, a second card, or heavier paper stock is usually what pushes a letter into the 2-ounce step.
The Letter Has to Be Letter-Shaped, Too
Weight is only half the calculation. To qualify for letter prices at all, an envelope must be rectangular and fall within these dimensions:
- Length: 5 to 11.5 inches
- Height: 3.5 to 6.125 inches
- Thickness: 0.007 to 0.25 inch
- Weight: no more than 3.5 ounces
Exceed any of those limits and the piece is priced as a large envelope (flat), starting at $1.69 for the first ounce and rising with weight up to 13 ounces. The dimension rules are covered in detail in USPS Letter Size and Weight Requirements.
When a 1-Ounce Letter Still Costs More Than One Stamp
Some letters weigh under an ounce but still cost more than $0.82, because they cannot run through USPS sorting machines and are charged a 49-cent nonmachinable surcharge on top of the letter price:
- Square envelopes (a 1-ounce square letter costs $1.31 total)
- Rigid or hard-to-bend envelopes, including anything with a photo or document that will not flex
- Envelopes with clasps, string, buttons, or other closures that stick out
- Unevenly thick or lumpy envelopes
- Envelopes addressed in a vertical (“portrait”) orientation
This is the trap many greeting cards fall into — see Do Greeting Cards Need Extra Postage? for the card-specific version of these rules.
Three Worked Examples
- A birthday card in a standard envelope weighs about 0.7 ounces sealed. One Forever stamp ($0.82) — done.
- A six-page signed agreement in a #10 envelope weighs about 1.6 ounces. That rounds up to the 2-ounce price of $1.11: one Forever stamp plus one 29-cent additional-ounce stamp.
- A square wedding invitation with a ribbon tie weighs 0.9 ounces — under an ounce, but square and non-flat, so it pays the letter price plus the 49-cent nonmachinable surcharge: $1.31 total, however light it feels.
Postcards and International Letters
Postcards. A standard postcard (up to 4.25 × 6 inches) mails for $0.65 with a postcard stamp. A Forever stamp works too, but you are spending $0.82 to buy $0.65 of postage. An oversized postcard is priced as a letter, starting at $0.82.
International letters. A 1-ounce letter to any other country costs $1.75. The cleanest payment is one Global Forever stamp, which is sold at that price and works for a 1-ounce letter or postcard to any destination worldwide. Heavier international letters are priced by destination group, so check the USPS price calculator before adding stamps.
A Worked Example: A 2.5-Ounce Letter With a Photo Inside
Suppose you are mailing a thick envelope: several pages of documents plus a printed photo, sealed and weighed at 2.5 ounces. Walk through the decision the way the price list does:
- Shape first. The envelope is a standard rectangular #10, flexible even with the photo inside, well within letter dimensions — so it stays a letter, not a flat.
- Round the weight up. 2.5 ounces rounds to the 3-ounce step. Ounces are not prorated.
- Build the price. First ounce $0.82, plus two additional ounces at 29 cents each: $0.82 + $0.29 + $0.29 = $1.40.
- Pay it exactly. One Forever stamp plus two additional-ounce stamps. (Two Forever stamps would be $1.64 — valid, but 24 cents wasted.)
Change one variable and the answer changes: if that photo makes the envelope too stiff to bend, the 49-cent nonmachinable surcharge joins the bill and the same letter costs $1.89. If the envelope were a 9 × 12 instead, it would be priced as a large envelope from the start. Weight, shape, and stiffness — in that order — are the whole calculation.
Letter, Postcard, or Large Envelope? A Side-by-Side
The same piece of paper can cost three different amounts depending on which category it is mailed as. For a 1-ounce piece at current prices:
| Category | 1 oz postage | What pushes a piece into it |
|---|---|---|
| Postcard | $0.65 | No envelope; within postcard size limits (up to 4.25 × 6 in) |
| Letter | $0.82 | Rectangular envelope within letter dimensions, up to 3.5 oz |
| Large envelope (flat) | $1.69 | Exceeds any letter dimension, or weighs over 3.5 oz, up to 13 oz |
The practical lesson: an oversized greeting card that misses letter dimensions by half an inch costs at least 87 cents more than the same card in a letter-size envelope. Choosing the envelope is choosing the price category — a point worth remembering when buying card stock, and one our USPS First-Class Mail: A Practical Guide covers across the whole service.
How to Check Before You Mail
- Weigh the sealed letter. A kitchen scale is accurate enough. Include the envelope and everything inside.
- Round up. Any fraction of an ounce moves you to the next price step.
- Check the shape. If it is square, rigid, or decorated with anything that sticks out, budget for the 49-cent surcharge or ask at the counter.
- When in doubt, ask. A Post Office retail counter will weigh and price a letter free of charge, and the USPS online price calculator gives the same answer for oversized or international pieces.
An Atlanta Sender’s Stack: Three Letters, Priced Step by Step
Most weeks, the “how many stamps” question is not abstract — it is a small stack of envelopes on a kitchen counter. Here is one from a sender in Decatur (30030), priced the way this guide recommends: shape first, then weight, then stamps.
- A rent check and a one-page letter to a landlord across town in Atlanta (30303). Standard #10 envelope, two sheets of paper, flexible. Sealed weight: about 0.6 oz. That is a plain 1-ounce letter — one Forever stamp, $0.82. The fact that it is only traveling a few miles saves nothing and costs nothing; letter prices are national.
- A family letter to relatives in Chicago, with six pages and two photo prints. Sealed and weighed: 2.3 oz, which rounds up to the 3-ounce step. Price: $0.82 + $0.29 + $0.29 = $1.40. Paid with one Forever stamp and two additional-ounce stamps. (A second Forever stamp would have put $1.64 on the envelope — 24 cents donated to no one.)
- A square graduation announcement going to Savannah. Only 0.8 oz — but square, so the 49-cent nonmachinable surcharge applies on top of the letter price: $1.31. One Forever stamp plus 49 cents in smaller stamps. The scale said “light”; the shape set the price.
Total for the stack: $3.53, and not one envelope over- or underpaid. Two practical Atlanta notes from doing this at home: a kitchen scale that reads to a tenth of an ounce settles almost every case on this page, and for the one envelope a year that still feels uncertain, any Post Office counter will weigh and price it free of charge — worth doing on the same trip when you are buying a book of stamps at the counter, at a grocery or drugstore checkout, or in a larger pack from a warehouse club in the metro area, all of which sell Forever stamps at face value.
Common Mistakes
- Rounding down. A 1.1-ounce letter is a 2-ounce letter for pricing purposes. Every fraction of an ounce moves you up a full step.
- Weighing before the envelope is finished. The envelope itself, a label, tape, and a late-added insert all count. Weigh the sealed, ready-to-mail piece.
- Paying for weight but forgetting shape. A light square envelope costs more than a heavier rectangular one — $1.31 versus $0.82 — because the surcharge ignores weight entirely.
- Reaching for a second Forever stamp. Additional-ounce stamps exist so the second and third ounces cost 29 cents, not another 82.
- Assuming distance matters. A letter to the next town and a letter to Hawaii cost the same at every weight step. Distance-based pricing applies to packages, not letters.
The Short Version
One Forever stamp for a normal letter up to 1 ounce. Add a 29-cent additional-ounce stamp for each ounce (or part of an ounce) above that, up to 3.5 ounces. Square and rigid letters pay a 49-cent surcharge, anything bigger or heavier is priced as a large envelope, and a letter abroad takes $1.75. If your envelope is a large one rather than a letter, How to Calculate Postage for Large Envelopes works through that pricing step by step.
Frequently Asked Questions
I don’t own a scale. How can I estimate?
Count the paper: roughly four or five sheets of ordinary copy paper in a standard envelope make an ounce. If your letter is close to that — or includes anything heavier than paper — have it weighed at a Post Office counter rather than guessing; the weighing is free.
Can I use Forever stamps on a large envelope?
Yes, their value counts toward the total, but a 1-ounce flat starts at $1.69, so one Forever stamp covers less than half. Add other stamps to reach the full amount.
What if I put too little postage on by mistake?
The letter is usually returned to you for the difference, or delivered with postage due owed by the recipient. Both outcomes cost more time than the stamp you saved.
Sources
The rates, dates, and rules in this guide were checked against these official USPS pages:
Related Guides
- Postage & Stamp Guides — the full library of postage and stamp help.
- What Is a Forever Stamp? — how the stamp behind these prices works.
- How Many Stamps Do Christmas Cards Need? — the same math applied to greeting cards.
- How to Calculate Postage for Large Envelopes — pricing once a piece outgrows letter size.
About the author — James Miller is a retired U.S. Postal Service employee whose career was in commercial mail, where he helped businesses prepare and send large-volume mailings. He edits Buy Holiday Stamps from Atlanta, Georgia. More about James and this site.
Last fact-checked against official USPS sources: November 2, 2026.