The short answer
To mail a letter in the US, put it in a rectangular envelope, write the recipient’s address in the lower middle of the front and your return address in the upper-left corner, and put a Forever stamp in the upper-right corner. One $0.82 Forever stamp pays for a standard letter up to 1 ounce (USPS retail price effective July 12, 2026, unchanged in the October 4, 2026 Notice 123). Seal the envelope, then leave it in your mailbox with the flag up, drop it in a blue collection box before the posted pickup time, or hand it to a Post Office clerk. Stamped mail that weighs more than 10 ounces or is thicker than 1/2 inch must be handed to a Post Office employee.
How to mail a letter in six steps
Sending a letter by post takes a few minutes once you have an envelope and a stamp. The order matters only in one place: USPS suggests putting the stamp on last, so a mistake in the address doesn’t waste it.
- Choose a rectangular envelope that fits your letter and stays flat.
- Write the delivery address in the lower middle of the envelope front.
- Write your return address in the upper-left corner.
- Put the letter inside and seal the envelope with its own glue or with tape.
- Put a Forever stamp, or enough postage for the weight, in the upper-right corner.
- Leave it in your mailbox, drop it in a blue collection box, or take it to a Post Office.
Choose an envelope that mails as a letter
USPS charges letter prices only for envelopes that are rectangular, made of paper, and between 5 × 3.5 inches and 11.5 × 6.125 inches, with contents that keep the piece no thicker than 1/4 inch. USPS uses the No. 10 business envelope, 4⅛ × 9½ inches, as its example of a standard envelope. You can fold the letter, but the envelope must stay flat.
To mail letter-size pages without folding them, use a large envelope such as a 9 × 12. USPS calls it a flat, and its postage starts at $1.69. A square envelope, or one that is rigid, lumpy, or closed with a clasp, string, or button, costs $0.49 more because it can’t go through the letter-sorting machines.
Decorated envelopes need extra care. USPS suggests putting envelopes with wax seals, strings, or ribbons inside another envelope, or paying the nonmachinable price and asking a Post Office clerk to hand-cancel them. Don’t put rigid items such as keys, coins, or flash drives loose in a paper envelope; USPS recommends a padded envelope or small box sent as a package.
What do I write when mailing a letter?
Write the delivery address parallel to the long edge in the lower middle of the envelope: the recipient’s name, then the street address with any apartment or suite number, then the city, state, and ZIP Code on the last line. Put your own name and address in the same format in the upper-left corner as the return address.
USPS asks for neat capital letters in pen or permanent marker, no commas or periods, and the ZIP+4 Code when you know it. If you are unsure of the ZIP Code, look it up before you seal the envelope.
Where to put the stamp on an envelope
The stamp goes in the upper-right corner of the envelope front, on the same side as the address. A Forever stamp costs $0.82 and covers a standard letter up to 1 ounce.
To work out how many stamps you need, weigh the sealed envelope on a kitchen scale, a postal scale, a self-service kiosk, or at the Post Office counter. As a rule of thumb, USPS says about four sheets of printer paper in a business-size envelope weigh 1 ounce. Each additional ounce costs $0.29 for letters up to 3.5 ounces, so a 2-ounce letter needs $1.11 in postage. You can buy stamps at a Post Office, a self-service kiosk, The Postal Store online, or retailers such as grocery and drug stores.
Two Forever stamps also cover a 2-ounce letter, but they pay $1.64 for $1.11 of postage. To pay closer to the exact amount, add low-value stamps: The Postal Store sells 1¢, 2¢, 3¢, 4¢, 5¢, and 10¢ stamps.
Where to mail your letter
Once the envelope is addressed, stamped, and sealed, USPS gives you four everyday places to send it. Pickup times on blue collection boxes are posted on the box’s label, can vary by day of the week, and may not apply on some days, such as the day before a holiday.
| Where | What to do | Good to know |
|---|---|---|
| Your own mailbox | Put the letter inside and raise the flag, if your mailbox has one. | Your carrier picks it up during normal delivery. |
| Cluster mailbox | Drop the letter in the outgoing mail slot. | USPS designates one compartment of a cluster box for outgoing mail. |
| Blue collection box | Drop it in before the last pickup time on the label. | Find boxes and their pickup times with the USPS Locations tool. |
| Post Office | Use the lobby drop, or hand it to a clerk at the retail counter. | A clerk can weigh it, sell postage, add extra services, and hand-cancel it. |
How to mail a letter at the Post Office, and when you must
Mail isn’t always postmarked on the day it is collected. If the postmark date matters, take the letter to a Post Office retail counter during retail hours and ask for a manual postmark; USPS applies it free of charge.
Some mail has to go to the counter. Under the Domestic Mail Manual, an item paid only with stamps that weighs more than 10 ounces or is more than 1/2 inch thick can’t go in a collection box or be left for your carrier; you must hand it to a Post Office employee. USPS returns improperly deposited items to the sender.
How do I mail a manila envelope?
A 9 × 12 or 10 × 13 manila envelope is a large envelope, or flat, to USPS: it is bigger than 11.5 × 6.125 inches but no larger than 15 × 12 inches and 3/4 inch thick. At current USPS prices (October 2026), First-Class Mail flats cost $1.69 for the first ounce and up to $5.24 at 13 ounces, the most First-Class Mail can weigh. Address and stamp it the same way as a letter.
The envelope must bend and stay evenly thick. If it is rigid, not rectangular, or lumpy, USPS charges package prices instead. Once a stamped manila envelope weighs more than 10 ounces or is more than 1/2 inch thick, take it to the counter rather than a collection box.
Optional: get proof that you mailed it
First-Class Mail has no tracking, and a stamped letter leaves you no receipt. If you may need to show that you sent it, buy an extra service at the counter before you mail it. A Certificate of Mailing, $2.45 with PS Form 3817, is evidence that you mailed the letter. Certified Mail, $5.55 plus postage, gives proof of mailing and the date and time of delivery or attempted delivery; Return Receipt adds the recipient’s signature.
How to send a letter without stamps or a printer
IRIS prints and mails individual letters for you. You upload a US Letter-size PDF, enter a sender name and return address and the recipient’s name and address, and review the document, addresses, options, and total before paying. IRIS prints the letter and mails it by USPS First-Class Mail to a US address, so you don’t need an envelope, stamps, or a mailbox.
A one-page black-and-white letter costs $3.20: a $3.00 service-and-postage fee plus $0.20 per black-and-white page, or $0.40 per color page. Certified Mail adds $6.95, and an electronic Return Receipt adds $2.91. IRIS doesn’t sell stamps, mail internationally, mail large (flat) envelopes, or enclose items such as checks, cash, or originals you hold; it prints the PDF you upload. It doesn’t guarantee a delivery date, and payment or order status isn’t proof of delivery.
Sources & further reading
Product details checked against the IRIS API contract when this article was published. Platform references can change; consult the linked documentation when implementing.
- USPS: How to Send a Letter or Postcard
- USPS Domestic Mail Manual 101: Physical Standards
- USPS Domestic Mail Manual 136: Deposit
- USPS Notice 123: Price List (Postal Explorer)
- USPS newsroom: U.S. Postal Service Recommends New Prices for July (April 9, 2026)
- USPS FAQ: What is a Collection Box?
- USPS Postal Explorer: Sending and Receiving Mail
- USPS Postal Explorer: Adding Extra Services
- USPS Postal Explorer: What Are You Mailing? Domestic
Published by IRIS Postal Forms, operated by Great Lakes Computing Office LLC. Send a correction.