Anything heavier than a standard one-ounce letter costs more to mail, and the amount it costs more is not obvious from looking at the envelope. A single Forever stamp covers one ounce. Past that point the price climbs in steps, and a second Forever stamp is almost always the wrong way to pay for it.
This page sets out what USPS charges above one ounce, what triggers the nonmachinable surcharge, and the point at which a letter stops being a letter and is priced as a large envelope instead. All rates are the USPS prices that took effect on July 12, 2026.
What USPS charges for a First-Class letter above one ounce
A First-Class Mail letter is priced by weight in whole-ounce steps, and the price of a First-Class Mail letter increases by twenty-nine cents for each additional ounce above the first ounce. The first ounce of a First-Class Mail letter costs eighty-two cents, which is the value a Forever stamp carries. A First-Class Mail letter may weigh up to three and one half ounces, and a piece of mail that weighs more than three and one half ounces is no longer priced as a letter.
| Letter weight | Postage due | How the price is reached |
|---|---|---|
| 1 ounce | $0.82 | Base First-Class letter rate |
| 2 ounces | $1.11 | $0.82 plus one additional ounce at $0.29 |
| 3 ounces | $1.40 | $0.82 plus two additional ounces at $0.29 |
| 3.5 ounces | $1.69 | $0.82 plus three additional ounces at $0.29 |
The practical consequence of the twenty-nine cent step is that a second Forever stamp overpays on a two-ounce letter. A second Forever stamp adds eighty-two cents of postage where only twenty-nine cents of postage is required, which means a second Forever stamp overpays a two-ounce letter by fifty-three cents. The correct combination for a two-ounce letter is one Forever stamp and one additional-ounce stamp, which together total exactly one dollar and eleven cents.
The nonmachinable surcharge, and what causes a letter to incur it
Weight is not the only reason a letter costs more than eighty-two cents. A letter that cannot be processed by automated USPS equipment incurs a nonmachinable surcharge of forty-nine cents, and the nonmachinable surcharge is charged in addition to the weight-based postage rather than instead of the weight-based postage.
USPS applies the nonmachinable surcharge to a letter for reasons of shape, rigidity and construction rather than for reasons of weight. A letter is treated as nonmachinable when the letter is square, when the letter is rigid or does not bend, when the letter contains an item that makes the thickness uneven, when the letter is closed with a clasp, a string, a button or a similar fastener, and when the length of the letter divided by the height of the letter falls outside the range of 1.3 to 2.5.
A square invitation envelope weighing one ounce is the case that catches most senders. A square invitation envelope weighing one ounce requires eighty-two cents of weight-based postage plus the forty-nine cent nonmachinable surcharge, for a total of one dollar and thirty-one cents. Detailed guidance for invitation mail is set out in the wedding invitation postage guide.
When a letter is priced as a large envelope instead
Mail that exceeds the dimensions permitted for a letter, or that exceeds three and one half ounces in weight, is classified as a large envelope, which USPS also refers to as a flat. A large envelope is priced from a different starting rate, and the first ounce of a large envelope costs one dollar and sixty-nine cents. Each additional ounce of a large envelope costs twenty-nine cents, which is the same additional-ounce rate that applies to letters. A large envelope may weigh up to thirteen ounces under First-Class Mail.
The nonmachinable surcharge does not apply to a large envelope, and a piece of mail that would incur the nonmachinable surcharge as a letter is sometimes cheaper to send in a large envelope. The comparison worth making is eighty-two cents plus the forty-nine cent surcharge against the one dollar and sixty-nine cent large envelope rate.
How to combine stamps without overpaying
Postage may be made up from any combination of valid stamps, and USPS accepts any stamp at the face value printed on the stamp, with a Forever stamp counting as the current First-Class letter rate of eighty-two cents. Overpayment is not refunded, so a combination that exceeds the postage due is money that is not recovered.
| Mail piece | Postage due | Efficient combination |
|---|---|---|
| 2-ounce letter | $1.11 | One Forever stamp plus one additional-ounce stamp |
| 3-ounce letter | $1.40 | One Forever stamp plus two additional-ounce stamps |
| 1-ounce square invitation | $1.31 | One Forever stamp plus one nonmachinable surcharge stamp |
| 1-ounce large envelope | $1.69 | Two Forever stamps plus five cents, or denominated stamps totaling $1.69 |
Older denominated stamps remain valid postage at the value printed on the stamp and may be combined with Forever stamps to reach an exact total. A drawer of low-value denominated stamps is often the cheapest way to make up the twenty-nine cent and forty-nine cent increments described above, because those increments are awkward to reach with Forever stamps alone.
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