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How Many Pages Can You Mail With One Stamp?
One Forever stamp covers 1 oz — about 4 sheets of 20 lb paper in a #10 envelope. See the page-count chart, the weight math, and when to add postage.
One Forever stamp covers a standard 1-ounce First-Class letter, which is roughly 4 sheets of regular 20 lb printer paper inside a #10 business envelope. Five sheets is the absolute borderline, and six or more almost always needs additional postage.
USPS does not count pages. It weighs the finished, sealed envelope. That is why the honest answer to “how many pages?” is always “it depends on the paper” — and why a kitchen scale settles the question in five seconds. For an exact figure on a specific envelope, the official USPS Postage Price Calculator will price it by weight, shape, and destination.
The 1-ounce rule, in plain numbers
A First-Class Mail letter is priced by the ounce, up to 3.5 ounces. As of the rates that took effect July 12, 2026:
| Letter weight | Postage | Stamps you can use |
| Up to 1 oz | $0.82 | 1 Forever stamp |
| Over 1 oz to 2 oz | $1.11 | Forever + 1 additional-ounce stamp |
| Over 2 oz to 3 oz | $1.40 | Forever + 2 additional-ounce stamps |
| Over 3 oz to 3.5 oz | $1.69 | Forever + 3 additional-ounce stamps |
Every additional ounce on a letter costs $0.29 in 2026. There is no grace zone: at 1.01 ounces, you owe the 2-ounce price.
What a page actually weighs
Here is where the 4-page rule of thumb comes from. A sheet of standard 20 lb copy paper weighs about 0.16 oz, and an empty #10 envelope weighs roughly 0.16 to 0.24 oz depending on the brand.
| Contents | Estimated total weight | Postage |
| Envelope + 1–3 sheets (20 lb) | 0.32–0.64 oz | 1 Forever stamp |
| Envelope + 4 sheets (20 lb) | ~0.80 oz | 1 Forever stamp (safe) |
| Envelope + 5 sheets (20 lb) | ~0.96 oz | 1 Forever stamp (borderline) |
| Envelope + 6 sheets (20 lb) | ~1.12 oz | Forever + additional ounce |
| Envelope + 3 sheets (24 lb resume paper) | ~0.75–0.84 oz | Usually 1 Forever stamp |
| Envelope + 2 sheets (65 lb cardstock) | ~0.76–0.96 oz | Borderline — weigh it |
| Envelope + folded greeting card + insert | 1.5–2 oz | 2 ounces of postage |
Five things that quietly push you over 1 ounce
- Heavier paper. 24 lb bond, resume stock, and glossy photo paper weigh noticeably more per sheet than 20 lb copy paper.
- Heavy ink coverage. Double-sided printing does not add sheets, but toner has weight, and full-page graphics on both sides add up.
- Inserts. A return envelope, a business-reply card, a photo, or a folded insert each adds real weight.
- A thicker envelope. Padded or linen-finish envelopes weigh more than a plain #10 before you put anything inside.
- Staples, clips, and tape. Small, but they count — and a rigid or lumpy envelope can trigger the nonmachinable surcharge even when it is under 1 ounce.
When a bigger envelope changes the price entirely
If you do not want to fold the pages, you move from letter pricing to flat (large envelope) pricing, which starts at $1.69 for the first ounce. A 9 x 12 envelope with three unfolded pages is not a “one stamp” letter — it is a flat.
Square envelopes, rigid mailers, and anything with clasps or buttons are treated as nonmachinable and carry a $0.49 surcharge on top of the letter price, bringing a 1-ounce square invitation to $1.31.
How to stop guessing
- Weigh the sealed envelope. A $12 postal scale pays for itself the first time it saves you a returned tax document.
- When in doubt, add an additional-ounce stamp. Overpaying by $0.29 is far cheaper than a letter that comes back two weeks late.
- Buy postage in the denominations you actually use. Most offices need mostly Forever stamps plus a small stack of additional-ounce stamps for the heavier pieces.
Frequently asked questions
How many sheets of paper equal 1 ounce?
About 4 to 5 sheets of 20 lb 8.5″ x 11″ paper, plus the envelope. USPS’s own rule of thumb is 4 sheets in a rectangular envelope for one Forever stamp.
Does double-sided printing need more postage?
It can. The sheet count stays the same, but heavy ink coverage adds weight, and dense double-sided pages can tip a 4-page letter past 1 ounce.
Can I put two Forever stamps on a 2-ounce letter?
Yes, and it is a common shortcut. Two Forever stamps is $1.64 of postage on a $1.11 letter — you overpay by $0.53, but the letter moves. An additional-ounce stamp ($0.29) is the cheaper way to do it.
What happens if I underpay?
USPS either returns the letter to you marked postage due, or delivers it and bills the recipient. We covered this in detail in What Happens If You Underpay Postage.
Stock up before you need to mail
If you mail more than a handful of letters a month, buying a few hundred Forever stamps at a time removes the “do I have stamps?” problem entirely. Browse discount Forever stamps, our 2013 Flags Forever stamps, and the full commemorative selection, or read how many Forever stamps to buy and how much you can save before you stock up.
Need the stamps? Browse our full shop of discount USPS Forever stamps.