Additional Ounce Stamps: How Much Weight Does a Forever Stamp Cover?
One Forever stamp covers a standard letter weighing up to one ounce. Every ounce after that costs $0.29 as of July 12, 2026, and that is exactly what one additional ounce stamp pays. A 2 oz letter needs $1.11 in total and a 3.5 oz letter, the heaviest piece that still counts as a letter, needs $1.69.
Two things change that math. A square, rigid or lumpy envelope adds a surcharge, and anything over 3.5 ounces or bigger than letter size is priced as a large envelope. Heavy invitations and holiday cards run into both.
How Much Weight Does a Forever Stamp Cover?
A Forever stamp covers one ounce of First-Class Mail in a letter-size envelope, and it's always worth the current one-ounce letter price: $0.82 as of July 12, 2026, no matter when or what you paid for it. That ounce only counts when the envelope also qualifies as a letter.
USPS rounds weight up, not down. Any fraction of an ounce is charged as a full ounce, so a card that weighs 1.1 ounces pays the 2-ounce price and one stamp won't be enough.
Size matters as much as weight. A letter must be 5 to 11-1/2 inches long, 3-1/2 to 6-1/8 inches high and no more than 1/4 inch thick, which a standard #10 business envelope or the envelope for a 5x7 card meets easily.
Extra ounces cost less than the first, which is why a second Forever stamp stretches a letter all the way to 3 ounces rather than stopping at 2.
USPS puts one ounce at about four sheets of regular letter paper in a rectangular envelope. Card stock, photos and inserts add up much faster, so a kitchen or postal scale is worth using on anything that feels thick.
For the one-ounce part of any letter, our 2026 US Flags Forever stamps are the everyday choice. The design is a photo of a knit flag with 1776 and 2026 printed beneath it, and it comes in booklets of 20, panes of 20 and coils of 100.
How Much Are Additional Ounce Stamps?
Each additional ounce on a stamped First-Class letter costs $0.29 as of July 12, 2026, according to the USPS price list. An additional ounce stamp pays that amount for one extra ounce. It doesn't replace the Forever stamp; it goes next to it.
USPS describes these stamps simply as postage for heavier mailpieces. The current design, the School Bus stamp released in January 2023, comes in panes of 20 and coils of 100 with no cent value printed on it, so it follows the extra-ounce rate rather than a fixed number.
At face value, a pane of 20 carries $5.80 in postage and a coil of 100 carries $29.00, so each stamp costs exactly the extra-ounce rate.
They're designed to ride along with a base stamp. On a 2 oz letter you'd use one Forever stamp and one additional ounce stamp; at 3 ounces, two; at 3.5 ounces, three. If most of your heavy mail sits at the same weight, a single stamp printed for that weight is tidier than building the total from pieces.
Letter Postage by Weight, 1 to 3.5 Ounces
This is what each weight step costs for a stamped First-Class letter, and which stamps add up to it without overpaying.
| Weight (not over) | Postage, July 12, 2026 | Exact stamp combination | Forever stamps only |
|---|---|---|---|
| 1 oz | $0.82 | 1 Forever | 1 ($0.82) |
| 2 oz | $1.11 | Two-ounce, or Forever + 1 | 2 ($1.64) |
| 3 oz | $1.40 | Three-ounce, or Forever + 2 | 2 ($1.64) |
| 3.5 oz | $1.69 | Forever + 3 | 3 ($2.46) |
In the table, "Forever + 1" means one Forever stamp and one additional ounce stamp. The exact combinations are worth aiming for because USPS doesn't refund overpayment on a single piece, and the Forever-only column shows how much extra goes on every envelope.
A three-ounce stamp such as the Saul Bellow Three Ounce stamp covers the 3 oz line on its own. It was issued in Chicago in February 2024 in the Literary Arts series, with the words Three Ounce printed vertically along its left edge.
There's no single stamp for 3.5 ounces, so the clean answer there is a Forever stamp plus three additional ounce stamps. If a piece sits right at the limit, weigh it again once it's sealed, since one more insert moves it into large-envelope pricing.
Postcards, international letters and other common cases are covered in our guide to how many stamps you need.
How Much Weight Do 2 Forever Stamps Cover?
Two Forever stamps add up to $1.64 as of July 12, 2026, which covers a standard letter up to 3 ounces. They fall 5 cents short at 3.5 ounces, where the price is $1.69, so in practice two Forever stamps fit anything over 1 ounce through 3 ounces.
The catch is overpayment. Two Forever stamps on a 2 oz letter pay 53 cents more than the $1.11 it needs, and on a 3 oz letter they pay 24 cents more. On one envelope that's small change, but on a full set of invitations it adds up, and two stamps take more of the corner on a printed envelope.
Two-ounce stamps solve both problems. A two-ounce stamp is always worth the two-ounce letter price, so one stamp pays a 2 oz letter exactly now and after the next price change.
The Wedding Blooms Two Ounce stamp is a good example: an ink-and-gouache bouquet with the words Two Ounce printed on it, issued in 2024 alongside the one-ounce Celebration Blooms stamp for reply envelopes.
We're an independent shop with no connection to USPS, and the two-ounce and three-ounce stamps we carry are surplus postage that we check sheet by sheet before listing.
How Many Additional Ounce Stamps to Mail a Letter?
Use one additional ounce stamp for each ounce, or part of an ounce, past the first, plus one Forever stamp. A 1.5 oz letter needs one, a 2.8 oz letter needs two and a 3.3 oz letter needs three.
Here's how to use additional ounce stamps on a heavy letter:
- Seal the envelope with everything inside, then weigh it.
- Round any fraction up to the next whole ounce.
- Put one Forever stamp in the upper right corner.
- Add one additional ounce stamp for each ounce after the first, next to the Forever stamp.
- Check the shape: square, rigid or lumpy envelopes also need the nonmachinable surcharge.
It takes three additional ounce stamps to match a Forever stamp. At July 2026 prices, three of them carry $0.87 against the $0.82 Forever price, while two carry only $0.58 and leave a one-ounce letter short.
That means you can use additional ounce stamps by themselves if they're all you have, as long as the total reaches the price. You'll give up 5 cents of postage on a one-ounce letter, so it works as a fallback rather than a habit.
Stacking is also where mistakes happen. Three or four stamps crowd a printed envelope and are easy to miscount across a batch, which is the main reason to use one two-ounce stamp when you mail the same 2 oz piece many times.
Are Additional Ounce Stamps Forever?
Recent ones work like Forever stamps, although USPS doesn't call them Forever stamps. When USPS announced the School Bus additional ounce stamp in January 2023, it described the stamp as non-denominated and said that, like a Forever stamp, it stays valid for the rate printed on it.
In practice, a non-denominated additional ounce stamp keeps covering one extra ounce after a price change, whatever you paid for it. USPS took the same approach with the Uncle Sam's Hat additional ounce stamp in 2017, which was non-denominated and sold at the extra-ounce rate of that time.
Older stamps with a cent value printed on them are different. They're worth exactly that amount and no more, so you combine them with other stamps to reach today's price.
Two-ounce and three-ounce stamps behave the same way for their weight: always worth the two-ounce or three-ounce letter price. That's why a Celebration Corsage two-ounce stamp from 2017 still covers a 2 oz letter today.
The same logic applies to one-ounce stamps bought years ago, which we cover in what a Forever stamp is worth today.
Nonmachinable Surcharge on Square or Rigid Letters
Weight isn't the only thing that sets the price. A letter that USPS sorting machines can't process pays a $0.49 nonmachinable surcharge as of July 12, 2026, on top of the price for its weight.
The Domestic Mail Manual lists the triggers. These are the ones that catch personal mail most often:
- Square or nearly square envelopes, where length divided by height is under 1.3
- Long, narrow envelopes, where that ratio is over 2.5
- Rigid pieces that don't bend easily
- Clasps, strings, buttons or similar closures
- Loose items inside, such as pens, keys or coins
- Plastic envelopes or plastic wrap
A square one-ounce card therefore needs $1.31. Nonmachinable surcharge stamps, the butterfly series, cover exactly that amount, and the Colorado Hairstreak Butterfly stamp is one of them, sold in panes of 20.
A square 2 oz invitation needs $1.60: $1.11 for the weight plus the $0.49 surcharge. One nonmachinable surcharge stamp plus one additional ounce stamp pays that exactly ($1.31 + $0.29), while two Forever stamps at $1.64 overpay by 4 cents and a two-ounce stamp alone falls 49 cents short.
More shapes and examples are in our article on when you need a non-machinable stamp.
When a Letter Becomes a Large Envelope
A letter becomes a large envelope, also called a flat, when it weighs more than 3.5 ounces or goes past any letter limit: 11-1/2 inches long, 6-1/8 inches high or 1/4 inch thick. A 9 x 12 envelope is a flat even with a single sheet inside.
As of July 12, 2026, flats cost $1.69 for the first ounce, $1.98 at 2 ounces, $2.27 at 3 ounces and $2.56 at 4 ounces, up to $5.24 at 13 ounces. Each extra ounce adds $0.29 through 8 ounces, so additional ounce stamps still work here.
A common rule of thumb says two Forever stamps cover a large envelope, but they don't. Two Forever stamps carry $1.64, 5 cents under the $1.69 one-ounce flat price, while a Forever stamp plus three additional ounce stamps pays it exactly.
Flats also have to stay flexible and evenly thick. A rigid, nonrectangular or lumpy large envelope pays package prices instead, so a small box or a bulky padded mailer won't qualify.
Before a batch goes out, weigh one finished piece, measure it against the letter limits and check its shape. If it's a 2 oz letter you'll send again and again, one two-ounce stamp per envelope is the simplest exact fit.
FAQ
Do additional Oz stamps expire?
No. Recent additional ounce stamps are non-denominated and stay valid for the additional ounce rate, and older ones with a printed cent value keep that value.
How many pieces of paper is 1 oz?
About four sheets of regular 8-1/2 x 11 inch paper in a rectangular envelope, by USPS's own estimate. Heavier paper, card stock or photos change that, so weigh anything that feels thick.
Is one Forever Stamp enough for a 5x7 card?
Usually, yes. A 5x7 card in its standard envelope fits letter size, so one Forever stamp covers it if it weighs one ounce or less and isn't square, rigid or lumpy.
How much postage do I need?
For a standard letter, $0.82 for the first ounce and $0.29 for each extra ounce, up to $1.69 at 3.5 ounces, as of July 12, 2026. Add the $0.49 surcharge for square, rigid or lumpy envelopes.