Quick answer: One ordinary Forever stamp covers an eligible domestic rectangular First-Class Mail letter weighing up to 1 ounce. For anything else, use the calculator below: the count changes with destination, mailpiece type, weight, dimensions and machinability.
Forever Stamp Calculator
Enter the finished mailpiece details, then select Calculate.
How to choose the correct mailpiece type
- Choose the destination: domestic or international.
- Classify the finished piece: postcard, letter, large envelope or package.
- Weigh it after assembly: include every insert, seal and decoration.
- Measure it: length, height and thickness can change the classification.
- Check machinability: square, rigid, lumpy or uneven letters can require a surcharge or another class.
Domestic letter examples
| Weight not over | 2026 postage | Ordinary Forever stamps only | Lower-overpayment combination |
|---|---|---|---|
| 1 oz | $0.82 | 1 | 1 Forever stamp |
| 2 oz | $1.11 | 2 | 1 Forever stamp + $0.29 additional postage |
| 3 oz | $1.40 | 2 | 1 Forever stamp + $0.58 additional postage |
| 3.5 oz | $1.69 | 3 | 2 Forever stamps + $0.05 additional postage |
A 4-ounce piece cannot use the ordinary letter table; it is priced as a large envelope or package according to its physical characteristics. A one-pound envelope is also outside First-Class Mail letter and domestic flat limits.
For a condition-by-condition answer, see when Forever stamps need extra postage.
When multiple Forever stamps are not the whole answer
Forever stamps contribute postage value, but the number of stamps does not determine the mail class. A rigid, oversized, thick, square, lumpy, heavy or international piece can require a different calculation. Whole Forever stamps may also overpay compared with adding smaller-denomination postage.
For the underlying rule, see how multiple Forever stamps can be combined on one envelope, including placement, overpayment and counter limits.
See the detailed 9×12 envelope example, learn when two Forever stamps work, or read the international Forever stamp guide.
Rate check: Calculator rates were verified September 9, 2026 against USPS Notice 123, effective July 12, 2026. Use the USPS Retail Postage Price Calculator for the final mailing decision.
For flexible-versus-parcel classification and a current 3-ounce example, read how many Forever stamps a bubble mailer needs.