Last reviewed: August 25, 2026. Postal prices can change; verify unusual pieces with USPS before mailing.
Quick answer: A machinable large envelope mailed within the United States costs $1.69 for the first ounce in 2026. Because one regular Forever stamp is worth $0.82, three Forever stamps cover a 1-ounce flat, but they overpay by $0.77. Exact-denomination postage is usually the cheaper choice. A 9×12 envelope is not automatically a flat: if it is rigid, lumpy, or too thick, USPS can price it as a package.
2026 large-envelope postage table
This table applies to a rectangular, uniformly thick First-Class Mail flat mailed domestically. “Forever stamps needed” rounds up to the next whole $0.82 stamp, so the last column shows why mixing denominations can save money.
| Weight | 2026 flat rate | Regular Forever stamps | Overpayment |
|---|---|---|---|
| 1 oz | $1.69 | 3 | $0.77 |
| 2 oz | $1.98 | 3 | $0.48 |
| 3 oz | $2.27 | 3 | $0.19 |
| 4 oz | $2.56 | 4 | $0.72 |
| 5 oz | $2.85 | 4 | $0.43 |
| 6 oz | $3.14 | 4 | $0.14 |
| 7 oz | $3.43 | 5 | $0.67 |
| 8 oz | $3.72 | 5 | $0.38 |
| 9 oz | $4.02 | 5 | $0.08 |
| 10 oz | $4.32 | 6 | $0.60 |
| 11 oz | $4.62 | 6 | $0.30 |
| 12 oz | $4.93 | 7 | $0.81 |
| 13 oz | $5.24 | 7 | $0.50 |
Does a 9×12 envelope count as a large envelope?
Usually, but size is only one part of the test. USPS treats a piece as a flat when it exceeds at least one letter maximum—6⅛ inches high, 11½ inches long, or ¼ inch thick—while staying within 12 inches high, 15 inches long, and ¾ inch thick. It must also be flexible, rectangular, and uniformly thick. A typical flexible 9×12 document envelope meets the size range.
A cardboard photo mailer, an envelope containing a pen, or a piece with a bulky clasp may fail the flexibility or uniform-thickness rules. In that case, do not rely on the flat table. Measure and weigh it, then use the postage calculator as a first check or take it to a Post Office counter for package pricing.
Three worked examples
Five sheets of paper in a 9×12 envelope
If the finished piece weighs no more than 1 ounce and remains flexible and even, the flat price is $1.69. Three regular Forever stamps provide $2.46. For less overpayment, ask for postage totaling $1.69.
A 3-ounce tax-return envelope
A qualifying flat costs $2.27. Three Forever stamps provide $2.46, an overpayment of $0.19. Weigh the sealed piece rather than estimating from the number of pages.
A rigid 9×12 photo mailer
Its dimensions look like a flat, but rigidity can move it into parcel pricing. The number of stamps then depends on the package’s weight, dimensions, and destination zone. See using Forever stamps on packages.
How to avoid returned mail
- Seal and weigh the complete envelope.
- Measure length, height, and thickness at the thickest point.
- Check that the contents bend and do not create a lump.
- Calculate the price for the actual mail class.
- If the classification is uncertain, have a postal clerk inspect it.
For a standard letter rather than a flat, use our broader Forever stamp quantity guide. Square or unusually shaped envelopes may instead need the nonmachinable surcharge.
Frequently asked questions
Can I use two Forever stamps on a large envelope?
Two regular Forever stamps are worth $1.64 in 2026, which is $0.05 short of the $1.69 1-ounce flat price. Add enough additional postage or use exact postage.
How many stamps go on a manila envelope?
“Manila” describes the envelope, not its mail class. A letter-size flexible piece may use letter rates; a larger qualifying piece uses flat rates; a rigid or uneven piece may be a parcel.
Does a clasp change the price?
A clasp alone does not create a universal rate. What matters is whether the sealed piece stays flexible, rectangular, and uniformly thick and can be processed safely.