Size ceiling
USPS caps a letter at 11-1/2 in long by 6-1/8 in high. Anything longer or taller in either dimension prices as a large envelope instead, up to a 15 in by 12 in outer limit.
Mail basics
How to address and mail an envelope
Three things go on the front: the recipient's address in the bottom center, your return address in the top left corner, and the stamp in the upper right corner. That layout comes straight from usps.com's own letter-sending guide, read 2026-09-01. What the stamp costs depends on weight and how stiff the envelope is, not the size printed on the box it came in.
USPS wording quotedNotice 123 pricesRead 2026-09-01
Three spots, one face
Recipient at the bottom, return address at the top left, postage at the top right.
Where everything goes
USPS's letter-sending guide lays out the front of an envelope in three fixed positions. Nothing about it changes whether the envelope is a plain #10 or a greeting card size, and getting a piece out of position is one of the more common reasons a letter gets delayed rather than lost outright.
| What it is | Where it goes | What it carries |
|---|---|---|
| Recipient address | Bottom center of the envelope | Full name, apartment or suite if applicable, street address, city, state and ZIP+4, each on its own line |
| Return address | Top left corner | Your own name, apartment or suite if applicable, street address, city, state and ZIP+4 |
| Postage | Upper right corner | A stamp, or a metered postage strip covering the same corner |
USPS also asks for dark text on a light background with the lines running parallel to the bottom edge of the envelope, the same legibility standard used for packages. Our USPS address format guide covers the field-by-field rules — capitals, abbreviations, unit numbers — that apply to either one.
Picking an envelope that stays at letter rates
USPS's own description is blunt about the category: envelopes are for sending flat, flexible things, like letters, cards, checks, forms, and other paper goods. Two limits decide whether a given envelope qualifies as a letter or gets bumped into large-envelope pricing.
Thickness and flex
A letter has to stay at or under 1/4 in thick and bend the way paper bends. A padded mailer, a clasp envelope, or anything stiffened by its contents fails that test even at letter dimensions.
Past 13 oz or too rigid
Once an envelope is too heavy or too stiff for large-envelope rules, USPS prices it as a package instead of mail. Our padded envelope guide covers that boundary in detail.
What the postage actually costs
From USPS Notice 123, effective July 12, 2026, read at pe.usps.com on 2026-09-01. A letter and a large envelope run on two separate price ladders, and the gap between them is real: the same weight can cost more than double once an envelope crosses from one class into the other.
| Class | Weight | Stamped price |
|---|---|---|
| Letter | 1 oz | 0.82 USD |
| Letter | 2 oz | 1.11 USD |
| Letter | 3 oz | 1.40 USD |
| Letter | 3.5 oz, class maximum | 1.69 USD |
| Large envelope | 1 oz | 1.69 USD |
| Large envelope | 13 oz, class maximum | 5.24 USD |
| Nonmachinable surcharge | Any letter that trips it | + 0.49 USD |
A clasp, string, button or loose lumpy contents all count as nonmachinable characteristics and add the surcharge even on an otherwise letter-rate piece. For a size-specific breakdown, our envelope cost guide covers the full postcard-through-large-envelope ladder, and the 6x9 envelope guide works through the letter-versus-large-envelope seam in detail. Once contents stop fitting the flat, flexible definition entirely, price the box instead through the calculator.
Buying the stamp and getting it into the mail
USPS names four places to buy postage: the Postal Store online, Post Office locations, self-service kiosks, and national retailers such as grocery and drug stores. Once the envelope is addressed and stamped, USPS lists three ways to actually send it.
Your own mailbox
Drop it in and raise the flag. The carrier already on the route picks it up on the next collection.
A blue collection box
Found on street corners and outside many Post Offices, picked up on a posted schedule.
A Post Office lobby drop
A slot inside or just outside the building, available whenever the lobby is open, sometimes around the clock.
Where these rules come from
- USPS, Send a Letter or Postcard — envelope selection, address placement, stamp placement, and where to buy postage and drop off mail. Read 2026-09-01.
- USPS, Notice 123 — letter, large envelope and nonmachinable surcharge prices. Effective July 12, 2026, read 2026-09-01.
USPS revises Notice 123 without much notice. Treat the prices above as what the price list stated on the date shown and check pe.usps.com before mailing a large batch.
Envelope questions, sourced from usps.com
How do I address an envelope?
USPS instructs writing the recipient's address in the bottom center of the envelope and the return address in the top left corner, both on separate lines with name, street address, city, state and ZIP, per usps.com read 2026-09-01.
Where does the stamp go on an envelope?
The upper right corner. USPS states the stamp goes in the upper right corner of the envelope, on the same face as the two addresses.
How much does it cost to mail an envelope?
0.82 USD to 1.69 USD for a letter up to 3.5 oz, or 1.69 USD to 5.24 USD for a large envelope up to 13 oz, per USPS Notice 123 effective July 12, 2026 and read 2026-09-01. A clasp, string or loose contents adds a 0.49 USD nonmachinable surcharge.
Where can I buy stamps?
The Postal Store online, Post Office locations, self-service kiosks, and national retailers such as grocery and drug stores, per usps.com read 2026-09-01.
How do I actually mail a finished envelope?
Put it in your own mailbox and raise the flag, drop it in a blue USPS collection box, or hand it in at a Post Office lobby drop, per usps.com read 2026-09-01.