How Many Stamps Do I Need?
A 1-ounce letter needs 1 Forever stamp. Its postage is $0.82 as of USPS Price List Notice 123 (edition effective October 4, 2026), and the Domestic Mail Manual says the postage value of each Forever stamp is the 1-ounce letter price. Heavier letters, large envelopes, postcards and international mail need more. Choose yours below for the exact postage, the number of Forever stamps and the overpayment.
Maintained by Archie Chang · Reviewed November 2, 2026 · Methodology & sources
Stamp calculator
You need 1 Forever stamp
Postage: $0.82 (Letters (stamped), weight not over 1 oz).
1 × $0.82 = $0.82, so the stamps overpay by $0.00. Each Forever stamp is counted at the 1-ounce stamped letter price.
Worked examples
Each row below comes from the same calculation as the calculator, with Forever stamps counted at $0.82 each and Global Forever stamps at $1.75 each. The count is the postage divided by the stamp value, rounded up.
| Mail piece | Postage | Stamps needed | Stamps total | Over the postage |
|---|---|---|---|---|
| 1-ounce letter | $0.82 | 1 Forever | $0.82 | $0.00 |
| 2-ounce letter | $1.11 | 2 Forever | $1.64 | $0.53 |
| 3.5-ounce letter | $1.69 | 3 Forever | $2.46 | $0.77 |
| 1-ounce letter, nonmachinable | $1.31 | 2 Forever | $1.64 | $0.33 |
| 1-ounce large envelope | $1.69 | 3 Forever | $2.46 | $0.77 |
| 3-ounce large envelope | $2.27 | 3 Forever | $2.46 | $0.19 |
| 13-ounce large envelope | $5.24 | 7 Forever | $5.74 | $0.50 |
| Postcard | $0.65 | 1 Forever | $0.82 | $0.17 |
| 1-ounce letter to Canada | $1.75 | 1 Global Forever | $1.75 | $0.00 |
| 2-ounce letter to Canada | $2.35 | 2 Global Forever | $3.50 | $1.15 |
The stamps total and the amount over the postage are arithmetic on the Notice 123 prices, not USPS figures. Postage by weight for every piece is on how much it costs to mail a letter.
How the count works
The Domestic Mail Manual sets the value of a Forever stamp:
“Forever stamps are sold for the price of the current First-Class Mail single-piece 1-ounce letter price. The postage value of each forever stamp is the current First-Class Mail single-piece 1-ounce letter price.”
So the calculator divides the postage by $0.82, the 1-ounce stamped letter price in Notice 123, and rounds up. First-Class Mail postage is charged by the ounce or fraction of an ounce, so a letter that weighs a little over 1 ounce pays the 2-ounce price:
“First-Class Mail - Per ounce or fraction thereof; any fraction of an ounce is considered a whole ounce. For example, if a piece weighs 0.5 ounces, the weight (postage) increment is 1 ounce.”
The total value of the stamps you put on must cover the postage:
“Unless excepted by standard, the total postage affixed must equal at least the postage charge for the class of the mail and, if applicable, the fee for the extra service requested.”
Letter, large envelope or postcard?
Letters up to 3.5 ounces pay the stamped letter prices. Over that weight a letter-size piece pays large envelope (flat) prices:
“Letter-size mail is:”
- Not less than 5 inches long, 3-1/2 inches high, and 0.007-inch thick. For pieces more than 6 inches long or 4-1/4 inches high, the minimum thickness is 0.009. Pieces not meeting the 0.009 thickness are subject to a nonmachinable surcharge under 1.2f.
- Not more than 11-1/2 inches long, or more than 6-1/8 inches high, or more than 1/4-inch thick.
“Not more than 3.5 ounces (First-Class Mail letter-size pieces over 3.5 ounces pay flat-size prices).”
“For weights over 3.5 ounces, see Large Envelopes prices.”
First-Class Mail letters and flats have a weight limit, which is where the tables stop:
“First-Class Mail (letters and flats} must not exceed 13 ounces.”
The calculator therefore stops at 13 ounces for domestic letters and large envelopes. Heavier pieces are outside these tables, and this page does not show package or parcel prices.
Is a 9 × 12 envelope a large envelope?
The Domestic Mail Manual defines flat-size mail by dimensions, flexibility and thickness:
“Flat-size mail is:”
- More than 11-1/2 inches long, or more than 6-1/8 inches high, or more than 1/4 inch thick, except as allowed for EDDM-Retail flats under 140. For general retail mailability, all pieces 1/4 inch thick or less must be a minimum of 5 inches long and 3-1/2 inches high and 0.007 inch thick.
- Not more than 15 inches long, or more than 12 inches high, or more than 3/4 inch thick.
- Flexible (see 2.3).
- Rectangular with four square corners or with finished corners that do not exceed a radius of 0.125 inch (1/8 inch). See Exhibit 201.1.1.1.
- Uniformly thick (see 2.4).
“Flat-size pieces must be flexible. Boxes—with or without hinges, gaps, or breaks that allow the piece to bend—are not flats.”
“Flat-size mailpieces must be uniformly thick so that any bumps, protrusions, or other irregularities do not cause more than 1/4-inch variance in thickness.”
A 9 × 12 envelope is 12 inches long, which is more than the 11-1/2 inches that ends letter size, and 9 inches high, so by length and height it is flat-size. Whether it is a large envelope also depends on its thickness (no more than 3/4 inch), flexibility and even thickness; that is our reading of the quoted standard, and USPS decides at the counter. A piece that fails those tests is priced as a parcel, which is outside these tables:
“Flat-size mailpieces that do not meet the eligibility standards in 2.3 through 2.4 are considered parcels and must pay the applicable parcel prices.”
“Large envelope-sized pieces that are rigid, nonrectangular, or not uniformly thick pay parcel prices.”
Postcards
A postcard pays the card price only if it meets the card dimensions; the calculator counts a card over 3.5 ounces at large envelope prices:
“Each card and part of a double card claimed at card pricing must be:”
- Rectangular.
- Not less than 3-1/2 inches high, 5 inches long, and 0.007 inch thick.
- Not more than 4-1/4 inches high, or more than 6 inches long, or greater than 0.016 inch thick.
- Not more than 3.5 ounces (Charge flat-size prices for First-Class Mail card-type pieces over 3.5 ounces.)
“Ineligible cards are subject to letter-size pricing.”
Nonmachinable letters
Notice 123 adds a surcharge of $0.49 for letters with certain characteristics:
“Letters that meet one or more of the nonmachinable characteristics in DMM 101.1.2 are subject to the $0.49 nonmachinable surcharge.”
The characteristics are listed in the Domestic Mail Manual:
“A letter-size piece is nonmachinable if it has one or more of the following characteristics (see 601.1.1.2 to determine the length, height, top, and bottom of a mailpiece):”
- Has an aspect ratio (length divided by height) of less than 1.3 or more than 2.5.
- Is polybagged, polywrapped, enclosed in any plastic material, or has an exterior surface made of a material that is not paper. Windows in envelopes made of paper do not make mailpieces nonmachinable. Attachments allowable under applicable eligibility standards do not make mailpieces nonmachinable.
- Has clasps, strings, buttons, or similar closure devices.
- Contains items such as pens, pencils, keys, or coins that cause the thickness of the mailpiece to be uneven; or loose keys or coins or similar objects not affixed to the contents within the mailpiece. Loose items may cause a letter to be nonmailable when mailed in paper envelopes; (see 601.3.3).
- Is too rigid (does not bend easily when subjected to a transport belt tension of 40 pounds around an 11-inch diameter turn).
- Is less than 0.009 inches thick if the mailpiece is more than 6 inches long or 4-1/4 inches high.
- Has a delivery address parallel to the shorter dimension of the mailpiece.
- Is a self-mailer that is not prepared according to 201.3.14.
- Is a booklet that is not prepared according to 201.3.16.
The surcharge rule in the Domestic Mail Manual, including its exceptions:
“The nonmachinable surcharge is charged per piece and applies to letter-size pieces that meet one or more of the nonmachinable characteristics in 101.1.2. Pieces mailed at the card price are not subject to the nonmachinable surcharge. An envelope weighing no more than one ounce with one enclosed standard optical disc no larger than 12 centimeters in diameter that is mailed as letter-size BRM (see 505.1.0) or PRM (see 505.2.0) and addressed to a company who sent the disc and BRM or PRM envelope to a subscriber as part of a round-trip-mailing (under 233.2.8) is not subject to the nonmachinable surcharge.”
The calculator adds the surcharge only to letters up to 3.5 ounces when you tick the box. For a letter-size piece over that weight, which pays large envelope prices, the sources above do not say whether the surcharge applies, so the calculator does not add it and says so.
International mail and Global Forever stamps
The Domestic Mail Manual gives the value of a Global Forever stamp:
“Commemorative stamps equal the current FCM single-piece 1-ounce stamped letter price. If labeled “Global Forever”, the current FCMI 1-ounce stamped letter price.”
The calculator counts Global Forever stamps at $1.75, the 1-ounce international letter price, which Notice 123 shows is the same in every price group. USPS lists the price group of each country (archived copy). Canada is price group 1 and Mexico is price group 2 in Notice 123. International letters are priced up to 3.5 ounces and international large envelopes up to 15.994 ounces in these tables; heavier pieces are outside them.
“Pieces that are rigid, nonrectangular, or not uniformly thick pay package prices.”
Additional-ounce stamps
Notice 123 has no price named “additional ounce”. The step from one letter weight to the next is $0.29 (arithmetic on the $0.82 and $1.11 rows). The Domestic Mail Manual lists a Forever stamp for “the current FCM additional-ounce price”, and Notice 123 gives no price under that name. The DMM list reads:
“The following Forever stamps will always be equal in value to the applicable price for the price category printed on them, at the time of use:”
- The current FCM additional-ounce price
- FCM non-machinable surcharge price
- FCM 2-ounce stamped letter price
- FCM 3-ounce stamped letter price
- FCM postcard price
This page does not state a selling price for it, because the sources checked gave none.
Frequently asked questions
How many stamps do I need for a letter?
A 1-ounce letter needs 1 Forever stamp: the postage is $0.82 as of USPS Price List Notice 123 (edition effective October 4, 2026), and the Domestic Mail Manual says the postage value of each Forever stamp is the 1-ounce letter price. A 2-ounce letter costs $1.11, which is 2 Forever stamps (the count is the postage divided by $0.82, rounded up, so the extra is $0.53). A 3.5-ounce letter costs $1.69, which is 3 Forever stamps.
How many stamps do I need for a large envelope?
A 1-ounce large envelope costs $1.69 as of USPS Price List Notice 123 (edition effective October 4, 2026). Paid only with Forever stamps that is 3 Forever stamps, which is $2.46 of stamps, $0.77 more than the postage (arithmetic). A 3-ounce large envelope costs $2.27, which is 3 Forever stamps. The calculator above counts any weight up to 13 ounces.
How many stamps do I need for a 9x12 envelope?
It depends on the weight and on whether USPS treats the piece as a large envelope (flat). The Domestic Mail Manual defines flat-size mail as more than 11-1/2 inches long or more than 6-1/8 inches high or more than 1/4 inch thick, and not more than 15 inches long, 12 inches high and 3/4 inch thick, flexible, rectangular and uniformly thick. A 9 × 12 envelope is 12 inches long, so by those dimensions it is flat-size if it is no thicker than 3/4 inch and is flexible and uniformly thick; that is our reading of the standard, and a rigid or box-like piece pays parcel prices, which are outside these tables. At large envelope prices a 1-ounce piece costs $1.69 (3 Forever stamps) and a 3-ounce piece $2.27 (3 Forever stamps).
How much postage do I need for a letter?
Stamped letters cost $0.82 up to 1 ounce, $1.11 up to 2 ounces, $1.40 up to 3 ounces, $1.69 up to 3.5 ounces as of USPS Price List Notice 123 (edition effective October 4, 2026). A letter-size piece over 3.5 ounces pays large envelope prices, so a 4-ounce piece costs $2.56 and the price rises to $5.24 for 13 ounces.
What is an additional ounce stamp?
Notice 123 lists letter prices by weight and has no row named additional ounce. The step from the 1-ounce letter price to the 2-ounce price is $0.29 (arithmetic: $1.11 minus $0.82). The Domestic Mail Manual lists, among Forever stamps that "will always be equal in value to the applicable price for the price category printed on them, at the time of use", one for "The current FCM additional-ounce price". The sources we checked on November 2, 2026 gave no selling price for it, so this page does not state one.
How many stamps do I need for an international letter?
Global Forever stamps are worth the 1-ounce international letter price, $1.75 as of USPS Price List Notice 123 (edition effective October 4, 2026). A 1-ounce letter costs $1.75 in every price group, so it needs 1 Global Forever stamp. A 2-ounce letter costs $2.35 to Canada and $2.60 to Mexico, so each needs 2 Global Forever stamps ($3.50 of stamps). The price group depends on the country.
Does a nonmachinable letter need more stamps?
It can. Notice 123 adds a $0.49 surcharge for letters that meet one or more of the nonmachinable characteristics in Domestic Mail Manual 101.1.2, such as a letter with a clasp or one that is too rigid. A 1-ounce letter with the surcharge costs $1.31, which is 2 Forever stamps instead of 1 Forever stamp.
Related pages
See how much it costs to mail a letter for postage by weight, and check whether the Post Office is open, whether mail is delivered and the 2026 and 2027 USPS holiday lists before you go.
More USPS postage and fee tools
Sources
- USPS Price List, Notice 123 (edition effective October 4, 2026) (archived copy)
- Domestic Mail Manual 604, Postage Payment Methods and Refunds (stamps) (archived copy)
- Domestic Mail Manual 133, Prices and Eligibility (retail First-Class Mail) (archived copy)
- Domestic Mail Manual 101, Physical Standards (archived copy)
- USPS.com, Mailing & Shipping Prices
Price table: Letters (stamped), Large envelopes (flats), Postcards and the international tables in Notice 123. Reviewed November 2, 2026.