The $0.29 Additional Ounce Stamp and When You Need One
An additional-ounce stamp costs $0.29. It is not postage on its own. It sits alongside a Forever stamp to cover a letter that weighs more than one ounce, and the arithmetic is the only part that needs explaining.
Work out what your envelope needs
| Letter weight | Postage needed | Total |
|---|---|---|
| 1 oz | 1 Forever | $0.82 |
| 2 oz | 1 Forever + 1 additional ounce | $1.11 |
| 3 oz | 1 Forever + 2 additional ounce | $1.40 |
| 3.5 oz | 1 Forever + 3 additional ounce | $1.69 |
3.5 ounces is the ceiling. Past that the piece stops being a letter in USPS terms and gets large-envelope pricing, which starts higher and climbs differently.
About five sheets of paper is where the second ounce starts
Most single-sheet letters stay comfortably under an ounce, which is why the additional-ounce stamp rarely comes up for ordinary post. It matters for multi-page documents, wedding invitations with inserts and reply cards, and anything on heavy stock. Five sheets of standard paper in a regular envelope is roughly the tipping point.
Weigh it if you are close. Underpaid mail is returned to the sender or delivered postage-due, and on a batch of invitations that means doing the whole job twice.
Why $0.29 has not moved while letters got dearer
The First-Class letter rate has risen nine times since 2019. The additional-ounce rate has held at $0.29 across several of those rounds. USPS prices each product separately rather than raising everything by one percentage, and the marginal cost of carrying a slightly heavier envelope is close to nothing once the letter is already in the network. The full pattern is in the rate change history.
Odd denominations are the easiest ones to forget about
Additional-ounce stamps get bought for one mailing and then sit in a drawer, because there is no everyday use for them. They do not expire and unused ones still have resale value. We buy them from the public alongside Forever stamps and older denominations, and pay within 3 business days of an accepted offer. Rates are on the sell unused stamps page.