How Much Does It Cost to Mail a Letter in the US?

Mailing a standard one-ounce letter anywhere in the United States costs $0.78 with a Forever stamp. That rate took effect July 13, 2025, and holds through at least early 2026. The full cost to mail a letter in the US can climb well past that if your envelope is heavy, oddly shaped, oversized, or sent with tracking or signature services.¹

Base Prices for a Letter or Postcard

The $0.78 Forever stamp covers a standard rectangular envelope up to one ounce. Each additional ounce runs $0.29, so a two-ounce letter costs $1.07 and a three-ounce letter costs $1.36.¹ The maximum weight for a First-Class letter is 3.5 ounces, which costs $1.65. Anything heavier gets reclassified as a large envelope or package at higher rates.²

A standard postcard costs $0.61.¹

If you print postage through a postage meter or commercial system instead of using a Forever stamp, the one-ounce rate drops to $0.74. Four cents per piece adds up if you send mail in volume.³

Forever stamps hold their value. If you bought a book at $0.73 before the July 2025 increase, each stamp still covers a one-ounce letter today. They don’t expire.

What Pushes the Cost Above $0.78

Weight

Every ounce past the first adds $0.29. A regular envelope with two or three sheets of printer paper usually stays under one ounce, but photos, extra pages, or cardstock will typically push you over. A kitchen scale settles the question.

Non-Machinable Shape

USPS sorting equipment expects standard rectangular envelopes. If yours can’t feed through the machines, you pay a non-machinable surcharge of $0.49 on top of regular postage.¹ Your letter counts as non-machinable if it has any of these traits:

Square or oddly proportioned. The length divided by height must fall between 1.3 and 2.5. Square envelopes fail automatically.
Too rigid to bend through sorting belts.
Clasps, strings, or buttons that stick out.
Uneven thickness from items like pens, keys, or coins inside.
A non-paper exterior, such as polybagged or plastic-wrapped pieces.

Square greeting cards trip people up most often. A birthday card in a square envelope costs $0.78 plus the $0.49 surcharge, or $1.27, even under one ounce.

Large Envelopes (Flats)

Envelopes taller than 6-1/8 inches, longer than 11-1/2 inches, or thicker than 1/4 inch get classified as “flats.” The first ounce costs $1.63, with additional ounces at $0.27 each for the first four ounces, $0.28 through nine ounces, and $0.30 through the 13-ounce maximum.⁴ Flats that are rigid or unevenly thick get bumped to parcel pricing, which is considerably more expensive.

Size Limits That Keep You at Letter Pricing

To qualify for letter rates, your envelope has to fall within these dimensions:⁵

Height: 3-1/2 inches minimum, 6-1/8 inches maximum.
Length: 5 inches minimum, 11-1/2 inches maximum.
Thickness: 0.007 inch minimum, 1/4 inch maximum.

Anything smaller than the minimums won’t be accepted. Anything larger gets reclassified as a flat or parcel. Standard #10 business envelopes (4-1/8 by 9-1/2 inches) and A2 greeting-card envelopes (4-3/8 by 5-3/4 inches) both fit comfortably.

Add-On Services for Important Mail

When you need proof of mailing or delivery, USPS offers several add-ons. Each fee sits on top of regular postage.

Certified Mail costs $5.30. You get a mailing receipt and electronic tracking, and the recipient signs on delivery. This is the standard choice for legal notices, lease terminations, and demand letters.¹
Return Receipt costs $4.40 for the physical green card or $2.82 electronic. It shows who signed and when. Most people pair it with Certified Mail.¹
Registered Mail starts at $19.70 and is the most secure option USPS offers, with the letter logged and locked at every point in the chain. The fee scales with declared value: $20.40 for items up to $100, $23.50 for items up to $500.¹

A one-ounce Certified letter with an electronic Return Receipt totals $8.90 ($0.78 + $5.30 + $2.82). That’s the usual setup for legal correspondence.

If you need guaranteed overnight or two-day delivery instead, a Priority Mail Express Flat Rate Envelope costs $33.25 at retail, with a legal-size version at $33.50. The price includes tracking, insurance, and a money-back guarantee if USPS misses the commitment.¹

Mailing a Letter Internationally

A one-ounce letter to any country costs $1.70 using a Global Forever stamp.⁶ Global Forever stamps never expire and hold their value through future price changes. First-Class Mail International letters can weigh up to 3.5 ounces, but anything over one ounce needs postage beyond the single stamp.

What Happens if You Underpay

An underpaid letter isn’t thrown away. For letters with a return address, USPS typically either delivers it and asks the recipient to pay the difference, or returns it to you marked “Returned for Additional Postage” so you can add what’s missing and resend. Non-machinable letters short on postage generally go back to the sender rather than out for delivery postage-due.

Quick Price Reference

One-ounce letter, Forever stamp: $0.78
One-ounce letter, metered: $0.74
Each additional ounce: $0.29
Postcard: $0.61
Non-machinable surcharge: $0.49
Large envelope, first ounce: $1.63
Global Forever stamp: $1.70
Certified Mail add-on: $5.30
Return Receipt: $4.40 physical, $2.82 electronic
Registered Mail: from $19.70
Priority Mail Express Flat Rate Envelope: $33.25

USPS adjusts prices regularly, often in January and July. The rates above are effective through at least early 2026. For the current figures at any time, the Notice 123 price list on the Postal Explorer site (pe.usps.com) is the authoritative source.⁴

1
United States Postal Service. Notice 123 – January 2026 Price Change
2
Postal Explorer. 201 Quick Service Guide
3
U.S. Postal Service. U.S. Postal Service Recommends New Prices for July 2025
4
Postal Explorer. Notice 123 – Postal Explorer
5
Postal Explorer. Sizes for Letters
6
USPS. First-Class Mail International