Practical Guide · One-Ounce Letters
What Can One Forever Stamp Cover?
Weight is only the first test. Shape, size, flexibility, and thickness also decide whether a single stamp is enough for an everyday letter.
Begin with the short answer
01 · The short answer
One stamp covers a standard one-ounce letter
One genuine, unused Forever Stamp covers the postage for a standard, machinable domestic First-Class Mail letter weighing no more than one ounce.
That sentence contains three separate tests: the piece must be light enough, it must fit the physical definition of a letter, and it must be suitable for ordinary automated processing. Passing the weight test alone does not always mean one stamp is sufficient.
The ordinary case
A flexible rectangular envelope, within letter-size dimensions and weighing no more than one ounce, is the clearest one-stamp example. A short personal letter, bill payment, thank-you note, or lightweight greeting card often fits this description.
The finished piece is no more than one ounce.
It stays within letter-size length, height, and thickness limits.
It is rectangular, flexible, evenly thick, and free of troublesome closures.
02 · Weight
The first ounce is included; later ounces are added
A Forever Stamp does not display a fixed cent amount because its mailing value follows the current stamped one-ounce First-Class Mail letter rate. On August 17, 2026, that value is 82 cents under the price list effective July 12, 2026.
For an ordinary stamped letter, each additional ounce currently adds 29 cents. The table below is a dated reference, not a permanent price promise.
| Finished weight | Stamped letter price | Value beyond one Forever Stamp | Practical note |
|---|---|---|---|
| Up to 1 oz | $0.82 | $0.00 | One Forever Stamp covers the basic rate. |
| Over 1 oz, up to 2 oz | $1.11 | $0.29 | Add the current additional-ounce amount. |
| Over 2 oz, up to 3 oz | $1.40 | $0.58 | Two additional-ounce increments are required. |
| Over 3 oz, up to 3.5 oz | $1.69 | $0.87 | 3.5 ounces is the letter-size First-Class Mail ceiling. |
Letter-size First-Class Mail pieces weighing more than 3.5 ounces pay flat-size prices. Physical size, flexibility, and uniform thickness can also move a piece into another category before it reaches that weight.
If your envelope is close to one ounce, use a postal scale or have the finished piece checked. The envelope, inserts, stickers, photographs, and decorations all count toward the final weight.
03 · Shape and size
A letter is defined by more than what is inside
To remain in the letter-size category, a mailpiece must fall within minimum and maximum dimensions. It must also be rectangular, with parallel opposite sides and generally square corners.
A piece that exceeds 11½ inches in length, 6⅛ inches in height, or ¼ inch in thickness may be treated as a large envelope or another mail category. Large envelopes use a different price table; as of July 12, 2026, the retail one-ounce flat price is $1.69.
The useful question is not only “How much does it weigh?” but also “What kind of mailpiece has this envelope become?”
Forever Stamp Guide · Editorial principle
04 · Processing
Why a light envelope can still need extra postage
Letter-processing equipment is designed for pieces with predictable proportions and flexibility. An envelope may be under one ounce yet require the nonmachinable surcharge because its shape, material, closure, rigidity, or contents make automated handling difficult.
An aspect ratio below 1.3 or above 2.5 is nonmachinable. A square envelope has a ratio of 1.0.
A piece that does not bend easily around processing equipment may not qualify as an ordinary machinable letter.
Keys, coins, pens, and other objects that create lumps or shift inside the envelope can change processing and mailability.
Clasps, strings, buttons, ribbons, and similar devices can make a letter nonmachinable.
Plastic wrapping or a nonpaper exterior can prevent a piece from qualifying as a machinable letter.
An address parallel to the shorter dimension is another listed nonmachinable characteristic.
Under Notice 123 effective July 12, 2026, a letter meeting one or more nonmachinable characteristics is subject to a 49-cent surcharge. This amount may change in a later price update.
05 · Everyday examples
Four envelopes, four different answers
These examples illustrate the reasoning process. They are not a substitute for weighing and checking the finished mailpiece.
A short personal letter
Two or three sheets of ordinary printer paper in a standard flexible rectangular envelope will often remain under one ounce and within letter dimensions.
A greeting card
A lightweight rectangular card may qualify. Thick cardstock, a separate photo, layered paper, or decorative inserts can push the piece over one ounce.
A square invitation
Even below one ounce, the square shape falls outside the machinable aspect-ratio range and generally triggers the applicable nonmachinable surcharge.
A large document envelope
An envelope exceeding letter dimensions may be priced as a large envelope. One Forever Stamp contributes value, but it does not by itself cover the current one-ounce flat price.
06 · Paper and inserts
“About four sheets” is a guide, not a guarantee
USPS product guidance describes one ounce as approximately four sheets of regular 8½-by-11-inch paper in a rectangular envelope. It is a useful mental estimate, but paper weight varies widely.
Copy paper may be lighter than stationery, cotton paper, photo paper, or heavy résumé stock. A lined envelope, return envelope, photograph, reply card, gift card, or brochure also changes the total.
Sheet count matters, but paper stock and size matter just as much.
Lining, padding, windows, and heavier paper add to the finished weight.
Photos, reply cards, stickers, ribbons, and seals can change both weight and machinability.
When accuracy matters, seal a sample exactly as it will be mailed and weigh the completed piece rather than weighing the contents alone.
07 · Combining value
More than one Forever Stamp can be used
Stamps can be combined to meet a required postage amount. At the current 82-cent value, two Forever Stamps contribute $1.64. That is more than the $1.11 price for an ordinary two-ounce stamped letter, but less than the current $1.69 price for a one-ounce large envelope.
Using two Forever Stamps may be convenient, but it can also overpay compared with using one Forever Stamp plus lower-denomination postage. The correct combination depends on the mailpiece category and the price in effect on the mailing date.
Adding stamps increases the postage value on the envelope. It does not convert a rigid piece into a machinable letter or change a large envelope into a standard letter.
08 · Visual notes
Design can match the letter; value follows the designation
Flag, floral, and celebration designs can serve very different occasions while carrying the same Forever designation. The artwork changes the opening gesture; the mailing calculation still depends on the finished envelope.
09 · Before mailing
A five-step one-stamp check
Run through this list after the envelope is completely assembled and sealed.
Include the envelope, every insert, and every decoration.
Confirm that all dimensions stay within letter-size limits.
Square and unusually long, narrow envelopes can be nonmachinable.
Rigid, lumpy, or shifting contents may require different handling.
Rates and surcharges can change after this article is published.
10 · Frequently asked
Common one-stamp questions
What does one Forever Stamp cover?
One Forever Stamp covers the current postage for a standard, machinable domestic First-Class Mail letter weighing no more than one ounce. Heavier, oversized, rigid, square, or otherwise nonmachinable pieces may need additional postage.
How many sheets of paper can I mail with one Forever Stamp?
Approximately four sheets of regular 8½-by-11-inch paper in a rectangular envelope is a common official estimate. Paper and envelopes vary, so weigh the finished piece when it is close to one ounce.
Can one Forever Stamp mail a greeting card?
Often, yes, when the card is rectangular, flexible, within letter dimensions, and no more than one ounce. Heavy cardstock, square envelopes, layered decorations, ribbons, or rigid features may require extra postage.
Can I use two Forever Stamps on one letter?
Yes. Two stamps contribute twice the current one-ounce letter value. That may be more than the exact amount required, so combining a Forever Stamp with lower-denomination postage can sometimes be more precise.
Does a square envelope need extra postage?
Generally, yes. A square envelope has an aspect ratio of 1.0, below the machinable range of 1.3 through 2.5, and is therefore subject to the applicable nonmachinable surcharge.
Can one Forever Stamp cover a large envelope?
Not at the current rate. As of July 12, 2026, a one-ounce large envelope costs $1.69, while one Forever Stamp contributes 82 cents. The stamp may be used as part of the total postage.
Does an old Forever Stamp still cover one ounce?
Yes, when it is genuine, unused, and bears the Forever designation. Its issue year does not reduce its current one-ounce letter value.
11 · Editorial record
Sources and date of reference
This article uses the domestic retail prices effective July 12, 2026, and was checked on August 17, 2026. Mailing standards and prices can change; the current official materials control.