One ordinary Forever stamp covers up to 1 ounce only when the mailpiece qualifies as a standard domestic First-Class Mail letter. It does not cover any weight without limit. Weight, dimensions, thickness, shape and flexibility all affect the postage category and final price.
Forever Stamp Weight Limit at a Glance
| Mailpiece | Weight | Does one ordinary Forever stamp cover it? |
|---|---|---|
| Standard machinable domestic letter | Up to 1 oz. | Yes |
| Standard machinable domestic letter | Over 1 oz. through 3.5 oz. | No; additional postage is required |
| Nonmachinable letter | Up to 3.5 oz. | Not by itself; a surcharge applies |
| Large envelope or flat | Up to 13 oz. in First-Class Mail | No; flat pricing applies |
| Package or international mail | Varies | No universal one-stamp rule |
How Many Ounces Does a Forever Stamp Cover?
For a qualifying domestic stamped letter, one ordinary Forever stamp covers the first ounce. The Forever feature protects its postage value when the one-ounce letter rate changes; it does not remove weight limits.
As of August 31, 2026, the stamped-letter prices are $0.82 through 1 ounce, $1.11 through 2 ounces, $1.40 through 3 ounces and $1.69 through 3.5 ounces. One ordinary Forever stamp is therefore enough only for the first row.
Size and Shape Conditions
A retail First-Class Mail letter must be rectangular and remain within the letter-size limits:
- Length: at least 5 inches and no more than 11½ inches.
- Height: at least 3½ inches and no more than 6⅛ inches.
- Thickness: at least 0.007 inch and no more than ¼ inch.
- Maximum letter weight: 3.5 ounces.
These are category limits, not a promise that one stamp covers every piece inside them. A square envelope, an unusually shaped piece, a rigid insert, an uneven item or other nonmachinable characteristic can trigger the current surcharge. A piece exceeding the letter limits may be charged as a large envelope or parcel.
What to Do When a Letter Weighs More Than 1 Ounce
- Weigh the complete sealed envelope, including every insert.
- Confirm it still qualifies as a letter by checking dimensions, thickness, shape and flexibility.
- Find the current price for its exact weight and category.
- Subtract the current value of the Forever stamp already applied.
- Add smaller-denomination postage for the difference, or use additional Forever stamps if overpayment is acceptable.
Do not assume one additional Forever stamp is required for every additional ounce. USPS prices additional letter ounces separately, so smaller-denomination postage is usually more precise.
Current Standard Letter Examples
| Weight not over | Current stamped-letter postage | Ordinary Forever stamp value | Additional postage needed |
|---|---|---|---|
| 1 oz. | $0.82 | $0.82 | $0.00 |
| 2 oz. | $1.11 | $0.82 | $0.29 |
| 3 oz. | $1.40 | $0.82 | $0.58 |
| 3.5 oz. | $1.69 | $0.82 | $0.87 |
The table assumes a standard machinable domestic letter. Add the current $0.49 nonmachinable surcharge when applicable. Rates can change, so verify them on the mailing date.
Frequently Asked Questions
Are Forever stamps good for any weight?
No. One ordinary Forever stamp covers the current postage for a qualifying one-ounce domestic letter. Other weights and mail categories require a different total postage amount.
Can a letter weigh exactly one ounce with one Forever stamp?
Yes, if it otherwise qualifies as a standard domestic First-Class Mail letter. “Up to 1 ounce” includes exactly 1.00 ounce.
What happens above 3.5 ounces?
The mailpiece is no longer priced as a First-Class Mail letter. Depending on its physical characteristics, it may qualify as a large envelope or parcel and needs postage for that category.
Does using two Forever stamps raise the weight limit?
It raises the postage value applied, but it does not change the physical 3.5-ounce maximum for letter pricing or remove size and nonmachinable rules.
Use the Forever stamp calculator and decision guide, compare what two Forever stamps cover, or review the envelope size limits.
Rates and standards checked August 31, 2026: USPS Notice 123, First-Class Mail weight and size standards, and Publication 25 physical standards for letters.
For the core value, validity, weight, and usage rules, see How Do Forever Stamps Work?.