Additional Ounce Postage Stamps: Rates & Uses in 2026
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An additional ounce stamp covers the extra weight past the first ounce of a First-Class letter, and right now it costs $0.29 each (Stamps.com, 2026). You pair it with a standard Forever stamp when your envelope tips past one ounce — a wedding suite, a six-page letter, a stack of photos. That's the whole job of additional ounce postage: bridge the gap so your mail doesn't come back stamped "postage due."
Most people meet these stamps the hard way. You drop a fat holiday card in the box, it lands back in your mailbox a week later, and now you're guessing. Let's fix the guessing.
Additional Ounce Postage Rate 2026
Each additional ounce on a First-Class letter is $0.29, on top of the $0.82 Forever stamp that covers the first ounce (Stamps.com, 2026). Large envelopes (flats) start at $1.63 for the first ounce and also add $0.29 per extra ounce. The additional ounce rate is the same whether your piece is a letter or a flat.
One caveat before you buy in bulk. USPS filed for new prices in April 2026, with changes proposed for July 2026 (USPS Newsroom, April 9, 2026). Rates listed here reflect the pre-July schedule. Before you stock up, check the current chart on USPS.com — a five-second look beats a returned envelope.
Postage Cost by Letter Weight
Here's the part you actually came for. This table maps weight to the exact stamps you need, First-Class letter rates:
| Letter weight | Total postage | Stamp combination |
|---|---|---|
| 1.0 oz | $0.82 | 1 Forever stamp |
| 2.0 oz | $1.11 | 1 Forever + 1 additional ounce |
| 3.0 oz | $1.40 | 1 Forever + 2 additional ounce |
| 3.5 oz (max) | $1.69 | 1 Forever + 3 additional ounce |
That 3.5 oz line is a hard wall. A First-Class letter can't weigh more than 3.5 ounces (USPS Postal Store, 2026). Cross it, and USPS reclassifies your piece as a large envelope or a package — different rates, different rules. More on that below.
A quick word on the math trap. Some folks slap two Forever stamps on a 2 oz envelope. That's $1.64 in postage for a job that needs $1.11. You've overpaid by 53 cents and you do it every single time. One Forever plus one additional ounce is the correct, cheaper combination. If you mail two-ounce envelopes regularly — invitations, contracts, newsletters — a dedicated 2 oz stamp prints the full $1.11 in a single peel, so there's nothing to stack and nothing to miscount.
Additional Ounce vs Forever Stamps
Short version: yes, additional ounce stamps hold their value like Forever stamps do. If USPS raises the additional ounce rate later, a stamp you bought at $0.29 still covers one additional ounce — it doesn't expire and doesn't need topping off. That's the same permanence Forever stamps carry, applied to the extra-weight tier.
The difference is what each one is for. A Forever stamp pays the first ounce. An additional ounce stamp pays for ounce two, three, and up to the 3.5 oz ceiling. They're partners, not substitutes. You'll see specialty designs too — the School Bus additional ounce stamp, for one — and those carry the same $0.29 additional-ounce value regardless of the artwork.
Using Additional Ounce Stamps Alone
Can you put an additional ounce stamp on an envelope by itself? Technically yes, but it only buys you $0.29 of postage. A one-ounce letter needs $0.82. So a lone additional ounce stamp on a standard letter leaves you 53 cents short, and that envelope comes back or arrives postage due.
Where a standalone additional ounce stamp does work is as a top-up. Say you already stuck a Forever stamp on, then realized the letter runs heavy. Add one $0.29 stamp for the second ounce and you're square. The stamp is a value, not a magic pass — it pays exactly $0.29 toward whatever the piece owes.
Common Mailing Scenarios
Weights are approximate; a $10 kitchen scale settles any doubt. Here's what shows up most:
- Wedding invitation with inner envelope, RSVP card, details insert — usually 2 oz. One Forever plus one additional ounce, or a single 2 oz stamp. Bonus: square envelopes catch a nonmachinable surcharge, so weigh and measure.
- Six-page typed letter, standard #10 envelope — often creeps to 2 oz once you fold it. Don't eyeball it; a 5-page letter can sit at 1 oz and a 7-page at 2 oz.
- Thick greeting card with a gift card tucked inside — the rigid card can trigger the nonmachinable surcharge even at 1 oz. Add postage for weight and for the bump.
- Small business reply mailing, tri-fold brochure plus reply card — commonly 2 oz. This is where a real 2 oz stamp pays off, because you're doing it in batches and every miscounted stack is a batch of returns.
Notice the pattern. Two ounces is the sweet spot for most "one Forever isn't enough" mail, which is exactly why a purpose-made two-ounce stamp exists.
When Letters Exceed 3.5 Ounces
Past 3.5 ounces, your letter isn't a letter anymore. USPS moves it to the large envelope (flat) category, which starts at $1.63 for the first ounce (Stamps.com, 2026). Same reclassification happens if the piece is rigid, lumpy, or too big for letter dimensions — thickness and shape matter as much as weight (USPS DMM standards).
So a heavy 4 oz newsletter in a 9x12 envelope isn't "a letter plus more stamps." It's a flat, priced from the flat schedule up. Weigh borderline pieces before you assume the letter rate applies.
Where to Buy Additional Ounce Stamps
The USPS Postal Store sells them directly, and your local post office window stocks them too. Buying online means you can print exact postage down to the cent, which beats hunting for stamp combinations — handy for odd weights.
There's a value angle worth naming. At Mailboxes of Flushing, we source unused, authentic stamps from closed businesses and inspect every one for unbent, flawless condition, so you get valid postage at a friendlier price than face value. For anyone mailing two-ounce pieces in volume, that adds up fast.
FAQ
What does "additional ounce" mean on a postage stamp?
It means the stamp pays for one ounce of weight beyond the first ounce of a First-Class letter or flat. You combine it with a Forever stamp — the Forever stamp covers ounce one, the additional ounce stamp covers each ounce after.
How much is additional oz USPS?
Each additional ounce is $0.29 as of 2026 (Stamps.com). USPS filed for new prices in July 2026, so confirm the current rate on USPS.com before buying in bulk.
Can I use 2 forever stamps for 2 oz?
Yes, but you'll overpay. Two Forever stamps cost $1.64, while the correct 2 oz postage is $1.11 — one Forever plus one additional ounce stamp, or a single 2 oz stamp.
How much is an extra ounce of U.S. postage?
$0.29 per additional ounce for both First-Class letters and large envelopes (flats), on top of the base stamp rate (Stamps.com, 2026).
Weigh the piece, match it to the table, and you'll never guess at postage again. If most of your mail lands at that two-ounce mark, skip the stacking altogether — browse the exact-value 2 oz stamp supplier options at Mailboxes of Flushing, where every stamp is inspected, authentic, and priced to save you money on the mail you send most.