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How much postage does an envelope need
One Forever stamp covers a standard envelope up to one ounce, which in practice is an envelope plus roughly four to five sheets of regular paper. Each additional ounce beyond that adds 29 cents. A large or thick envelope, anything bigger than a standard number 10 or over a quarter inch thick, is priced as a Flat starting at $1.69 rather than as a Letter. Rates shown here reflect the July 12, 2026 increase.
Checked July 30, 2026/6 min read
Written by Claire PostReviewed against USPS Publication 28
What is on this page6 sections
Postage math looks simple until an envelope runs slightly heavier or slightly larger than the standard case, and then it becomes two separate questions: how many ounces, and does this even still count as a Letter. Getting either one wrong means underpaid mail, which typically gets delayed or bounced back rather than delivered anyway with a note.
The rates below reflect the most recent USPS increase, effective July 12, 2026. Rates change periodically, sometimes more than once in a year, so the date matters as much as the numbers themselves.
Step by step
Use one Forever stamp for a standard letter up to one ounce
This covers the large majority of everyday mail: a card, a short letter, a one or two-page document in a standard envelope.
Add 29 cents for each ounce beyond the first
A 2-ounce letter needs $1.11 total, a 3-ounce letter needs $1.40, and so on, up to the 3.5-ounce Letter-rate limit.
Know roughly how many sheets fit in one ounce
A standard sheet of paper weighs about 0.16 ounces, and a standard envelope weighs about 0.15 ounces on its own. That leaves room for roughly four to five sheets before crossing one ounce, though it is worth weighing anything that feels borderline rather than guessing.
Use Flat rate postage for anything larger or thicker than a standard letter
A 9x12 envelope, or anything thicker than about a quarter inch, is priced as a Flat starting at $1.69 for the first ounce, not the Letter rate.
Use the international rate for mail leaving the country
An international letter up to one ounce costs $1.75, separate from and higher than the domestic Forever stamp rate.
Quick reference
| Mail type | Rate (July 2026) |
|---|---|
| Domestic letter, first ounce | $0.82 (Forever stamp) |
| Domestic letter, each additional ounce | +$0.29 |
| Large envelope / Flat, first ounce | $1.69 |
| Domestic postcard | $0.65 |
| International letter, first ounce | $1.75 |
| International postcard | $1.75 |
Special cases
The rule above covers most people. Here is what changes for the rest.
Does a Forever stamp still work if I bought it before a rate increase?
Yes. A Forever stamp is valid for a one-ounce First-Class letter regardless of when it was purchased or how many rate increases have happened since, which is the entire point of the Forever design. You never need to add a penny stamp to a Forever stamp because of a rate change on standard letter mail.
How many sheets of paper can I fit in one envelope before I need extra postage?
Roughly four to five standard sheets of regular printer paper, plus the envelope itself, generally stays within one ounce, but this varies with paper weight and envelope material. Heavier cardstock or a padded envelope reaches that limit much faster. If a mailing feels close to the edge, weighing it on a kitchen scale is more reliable than guessing, since a piece mailed with insufficient postage gets delayed or returned rather than simply delivered late.
Does a colored or padded envelope need different postage than a plain white one?
Not because of color, but weight and thickness both count toward the ounce total regardless of what the envelope looks like. A padded or heavier-stock envelope reaches the next weight threshold faster than a plain lightweight one, so check the actual weight rather than assuming a fancier envelope is postage-neutral.
Key terms on this page
- Forever stamp
- A First-Class stamp valid for a standard one-ounce letter regardless of future rate increases, priced at whatever the current one-ounce rate is when purchased.
- Additional ounce rate
- The per-ounce charge added for each ounce beyond the first, currently 29 cents, up to the 3.5-ounce Letter-rate maximum.
- Flat
- A USPS mail category for envelopes exceeding standard Letter size or thickness limits, priced higher than a Letter, starting at $1.69 as of July 2026.