A typical 9×12 or manila envelope is evaluated as a large envelope (flat), not as a standard letter. The retail price for a qualifying one-ounce flat starts at $1.69 effective July 12, 2026. The number of stamps depends on the finished item and the values you use.
Why “two stamps” is not a universal answer
Two domestic Forever stamps currently provide $1.64, which is 5¢ short of the one-ounce flat price. Three provide $2.46 and overpay. A precise denomination combination or postage printed at a Post Office avoids both underpayment and needless overpayment.
A flat must remain a flat
- Measure the filled and sealed envelope, not the empty package label
- Check thickness and uniformity
- Make sure it is flexible enough for flat processing
- Weigh all documents, folders and fasteners together
- Rigid contents, lumps or excessive thickness can make it a package
Common examples
| Finished piece | Likely next step |
|---|---|
| Flexible 9×12 documents, up to 1 oz | Check flat eligibility; base price $1.69 |
| Flexible 9×12 over 1 oz | Use current flat weight table/calculator |
| Rigid photo mailer | May be a package; do not use flat price automatically |
| Small square invitation | Evaluate as nonmachinable letter, not merely “large” |
| Envelope with merchandise | Class and service may change; verify at USPS |
Classify the finished mailpiece first
- Seal the actual contents inside the envelope.
- Measure length, height and thickness; weigh the completed piece.
- Check shape, aspect ratio, rigidity, clasps, uneven thickness and other nonmachinable features.
- Choose the correct mail class, destination and any extra service.
- Then meet the required dollar postage with valid unused stamps or another accepted payment method.