How Many Stamps Do I Need to Mail a Letter?

How many stamps do you actually need to send a letter? The short answer is just one Forever stamp for a basic 1-ounce domestic letter. But what happens if your envelope is heavy, rigid, or oddly shaped? Factors like weight, size, and destination all affect your total cost, so weighing your letter first is key to getting it right.

How Many Stamps Do You Need?

One Forever stamp pays the 1-ounce First-Class Mail letter price, regardless of the price printed when you bought it. As of July 12, 2026, that value is $0.82. Each extra ounce costs $0.29, and a machinable domestic letter can weigh no more than 3.5 ounces.

Here is the practical answer for a rectangular, flexible envelope mailed within the United States.

Sealed letter weight	Postage required	Cost-effective stamp combination	Forever stamps alone
Up to 1 oz	$0.82	1 Forever stamp	1
Over 1 oz through 2 oz	$1.11	1 Forever + 1 additional-ounce stamp	2, with overpayment
Over 2 oz through 3 oz	$1.40	1 Forever + 2 additional-ounce stamps	2, with overpayment
Over 3 oz through 3.5 oz	$1.69	1 Forever + 3 additional-ounce stamps	3, with overpayment

 

These figures come from the USPS price list effective July 12, 2026. Postal rates change, so check the USPS Price Calculator before sending a valuable letter or preparing a large batch.

Count postage by value, not by pieces of paper stuck to the envelope. Two Forever stamps will cover a 2-ounce letter, but one Forever stamp plus one additional-ounce stamp reaches the required value without wasting postage.

What Changes Your Stamp Count?

Four details determine whether the table applies: the sealed weight, the envelope dimensions, its ability to pass through sorting equipment, and the destination. A light envelope can still cost more if its shape makes it nonmachinable.

·  Weight includes the envelope, every sheet, cards, photos, labels, and return envelopes.

·  Size decides whether USPS prices the mailpiece as a letter, a large envelope, or a package.

·  Shape and flexibility affect whether automated equipment can process it.

·  Destination separates domestic letter rates from international postage.

A paper envelope qualifies for letter pricing only when it is rectangular and no more than 11.5 inches long, 6.125 inches high, and 0.25 inch thick. Go beyond a letter limit and the same contents may be charged as a large envelope or package.

Square invitations, rigid cards, uneven envelopes, and mail with clasps or raised wax seals may incur a $0.49 nonmachinable surcharge under the July 2026 rates. That surcharge is separate from extra-ounce postage. A 2-ounce square invitation can require both charges.

How Do You Calculate Postage?

The safest calculation takes less than a minute when you have a scale. Prepare one finished envelope exactly as it will enter the mailstream.

1. Seal the complete letter. Include the card, photographs, reply envelope, stickers, and every other insert.

2. Weigh the envelope. Use a scale that reads tenths of an ounce. A reading of 1.01 ounces is above the 1-ounce tier.

3. Measure and handle it. Check the length, height, and thickness, then make sure the envelope is rectangular, evenly thick, and flexible.

4. Identify the destination. The standard one-stamp answer covers a qualifying domestic letter, not an international one.

5. Add the required value. Use a Forever stamp for the first ounce and additional-ounce postage for added weight.

If the scale reading sits on a boundary, verify the letter at a Post Office rather than assuming it will pass. The same advice applies to wedding invitations: assemble and seal one sample, then have that exact sample checked before stamping the rest.

How Many Pages Fit One Stamp?

About four sheets of standard 8.5-by-11-inch printer paper in a business envelope often remain within 1 ounce. USPS presents that as an estimate, not a mailing guarantee.

Paper weight changes the result quickly. Four sheets of 20-pound copy paper are not equivalent to four sheets of heavy résumé stock. A greeting card, photograph, brochure, or return envelope also adds more weight than another ordinary page might.

Use this shortcut only for routine correspondence:

Contents	Likely result	Best next step
1–4 sheets of copy paper	Often at or below 1 oz	One Forever stamp may be enough
Heavy stationery or card stock	May exceed 1 oz	Weigh the sealed envelope
Photos, cards, or reply envelopes	Weight varies	Do not estimate by page count
Thick or rigid inserts	Pricing may change	Check size and machinability too

 

Mail that must arrive on time is a poor place to save thirty seconds. Weigh it.

When Is One Stamp Not Enough?

One stamp stops being the default as soon as the finished mailpiece exceeds the standard 1-ounce machinable-letter rules.

The letter weighs more than 1 ounce. Add postage for every extra ounce or fraction of an ounce. If heavier correspondence is routine, keeping 2-ounce stamps available can make preparation quicker.

The envelope is nonmachinable. Square, rigid, lumpy, vertical, or uneven letters may need a surcharge even below 1 ounce. Decorative closures can be the deciding factor.

The envelope is too large. A 9-by-12-inch document envelope usually falls under large-envelope pricing, which starts at $1.69 for 1 ounce under the July 2026 schedule. A rigid or nonuniform flat may be priced as a package instead.

The destination is outside the United States. International letter prices depend on destination, weight, and dimensions. A qualifying 1-ounce letter may use a Global Forever stamp, but a domestic Forever stamp by itself does not cover the typical international rate.

Can You Use Extra Forever Stamps?

Yes. Valid unused stamps can be combined as long as their total value meets or exceeds the required postage. USPS does not require a particular physical combination.

Extra Forever stamps are convenient, though often expensive. Under July 2026 prices, two Forever stamps represent $1.64. A standard 2-ounce letter requires $1.11, so that combination overpays by $0.53. One Forever stamp and one additional-ounce stamp is the tighter match.

If you need to confirm the current value of a Forever stamp, use the separate Forever Stamp price guide. Keeping price details there avoids mixing a rate-update question with this letter-postage calculation.

Before mailing, seal the envelope, weigh it, and confirm its shape. For ordinary 1-ounce correspondence, Mailbox Flushing offers First-Class stamps; for mixed household mail, keeping both Forever and additional-ounce stamps nearby gives you a better chance of paying the exact amount.

Frequently Asked Questions

Do letters need one or two stamps?

Use one Forever stamp for a standard domestic letter weighing no more than 1 ounce. Use more postage when the sealed letter is heavier, nonmachinable, oversized, or international.

Can three stamps mail three ounces?

Three Forever stamps provide more value than a standard 3-ounce domestic letter requires. One Forever stamp plus two additional-ounce stamps is the more economical July 2026 combination.

Are two stamps enough for large letters?

Not always. Large-envelope postage depends on weight, dimensions, thickness, and flexibility, so two stamps may underpay or overpay; use the USPS calculator for the finished mailpiece.

How can you spot nonmachinable letters?

Square, rigid, lumpy, uneven, or unusually oriented envelopes may be nonmachinable. When the shape is unclear or the envelope has a raised closure, ask a postal clerk to check one finished sample.