How to Address Mail Correctly in the USA: A Complete Guide

• USPS sorting machines read addresses with OCR, so use ALL CAPS and avoid punctuation in the address block.
• The standard format is: name, street address (with apartment or suite), then city, state, ZIP on the last line.
• Use the two-letter state abbreviation (CA, NY, TX) — never the full state name.
• ZIP+4 (like 90210-1234) is optional but improves delivery accuracy and speed.
• Military mail uses APO, FPO, or DPO instead of city and state — never use the host country.
• For multi-unit buildings, include the apartment, suite, or unit number on the same line as the street address.
• Online mailing services like PostPal validate every address automatically, so you can't skip a unit number or mistype a ZIP.

Every year, millions of pieces of mail are delayed or returned because of addressing errors. USPS uses automated sorting machines that scan envelopes with optical character recognition (OCR). When an address doesn't follow the standard format, your mail kicks out for manual handling — which means delays, or worse, a return-to-sender stamp.

This guide covers exactly how to format addresses for US mail, the most common mistakes, and how to skip the whole problem with a few clicks.

A properly formatted US address has three (sometimes four) lines, in this order:

Recipient's Address (Center of Envelope)

Breaking It Down:

• Line 1: Recipient's name (person or business)
• Line 2: Street number, street name, and apartment or suite
• Line 3: City, two-letter state abbreviation, and ZIP code

Return Address (Top-Left Corner)

Your return address follows the same format and lives in the upper-left corner of the envelope. It's where your letter goes if delivery fails — so don't skip it.

USPS recommends ALL CAPS and no punctuation in the address block. It looks a bit shouty, but it gives the OCR scanners the cleanest possible read.

Always use the official two-letter USPS state abbreviation. Spelling out "California" or using "Calif." will confuse the sorting machines.

Important: All 50 states, DC, and US territories (Puerto Rico, Guam, US Virgin Islands) have their own two-letter codes. The USPS website maintains the official list if you're unsure.

A US ZIP code is five digits — like 90210. The optional ZIP+4 adds a hyphen and four more digits: 90210-1234. The extra four digits identify a specific block, building, or PO Box, and they help your mail land in the right slot faster.

Key Rules for ZIP Codes:

• Always five digits, sometimes followed by a hyphen and four more
• The first digit indicates a broad region (0 for the Northeast, 9 for the West Coast)
• Leading zeros matter — Massachusetts ZIPs start with 01, not 1
• ZIP+4 is optional but recommended for business mail and bulk mailings

The first digit roughly maps to a region of the country: 0 for the Northeast, 9 for the West Coast, with the middle digits filling in the geography in between. If you don't know the ZIP+4, the five-digit ZIP is fine — USPS will fill in the rest from the street address.

If your recipient lives in an apartment, condo, or office suite, the unit number must be on the address. Without it, the carrier can't figure out which mailbox is theirs. USPS prefers the unit on the same line as the street address, after the street name:

Standard USPS unit designators include APT (apartment), STE (suite), UNIT, BLDG (building), FL (floor), and RM (room). Skip the "#" symbol — USPS recommends using the abbreviation (APT 5B) rather than "#5B".

Not all addresses follow the standard street format. Here's how to handle the common special cases.

PO Box Addresses:

Use "PO BOX" (no periods) followed by the box number. If the recipient has both a PO Box and a street address, USPS will deliver to whichever appears on the line directly above the city/state/ZIP.

Military Mail (APO, FPO, DPO):

For service members and embassy personnel, the city is replaced with APO (Army/Air Force), FPO (Navy/Marine Corps), or DPO (State Department). The state field uses one of three codes:

• AA - Armed Forces Americas
• AE - Armed Forces Europe, Middle East, Africa, Canada
• AP - Armed Forces Pacific

Never write the host country (Germany, Japan, etc.) on military mail. APO/FPO/DPO addresses are domestic from a USPS rate perspective, and the country line will route the letter into the international system instead.

General Delivery:

For recipients without a fixed address in a town, you can use General Delivery at the local post office:

These are the most frequent errors that cause mail delivery problems:

1. Missing or Wrong ZIP Code

The ZIP code is the most critical element for sorting. A missing or incorrect ZIP can route your letter to the wrong state entirely.

2. Missing Apartment or Suite Number

For multi-unit buildings, the unit number is essential. Without it, mail carriers can't deliver to the correct mailbox.

Correct: 123 MAIN ST APT 5

Incorrect: 123 MAIN ST (missing unit)

3. Spelling Out the State

USPS sorting machines expect the two-letter abbreviation. Writing "California" or "Calif." instead of "CA" can slow down processing.

4. Illegible Handwriting

OCR scanners and human carriers both need to read the address clearly. Sloppy handwriting causes delays and misdeliveries.

5. Punctuation in the Address Block

Skip commas, periods, and other punctuation in the recipient address. USPS prefers a clean, all-caps block: BROOKLYN NY 11215, not Brooklyn, N.Y. 11215.

6. Wrong Order of Elements

Putting the city before the street, or the ZIP before the state, will confuse sorting systems and likely require manual handling.

When sending mail abroad, you need to write the destination country on the last line, in capital letters, in English. The internal format follows the destination country's convention.

To Canada:

To the United Kingdom:

Key Tips for International Mail:

• Always write the country name on the last line, in capital letters and in English
• Use the destination country's native postal code format (Canadian postal codes have a space, UK codes are alphanumeric)
• Don't add "USA" — your return address already shows the origin
• USPS International First-Class Mail typically takes 7-14 business days, though delivery time varies widely by destination

Even with a guide in hand, addressing errors are easy to make. One typo in a ZIP, a missing apartment number, or an illegible 5 vs. S, and your letter ends up in the wrong mailbox — or back in yours.

This is where online mailing services shine. Services like PostPal use structured forms with built-in validation to make addressing errors nearly impossible.

How PostPal Prevents Addressing Errors:

• Structured Forms: Separate fields for each address component mean nothing gets skipped
• ZIP Validation: The system checks that the ZIP matches the city and state
• Required Fields: You can't submit without filling in essential information like unit numbers
• Automatic Formatting: Addresses are printed in proper USPS format every time, in ALL CAPS, no punctuation
• No Handwriting Issues: Printed labels are perfectly legible to both OCR scanners and humans

Why This Matters

When you fill out an online form, the system guides you through each required field. It won't let you forget the ZIP or skip the apartment number. And because addresses are printed by machine, there's zero risk of a smudged 8 looking like a 3.

It's addressing made foolproof.

Properly addressing mail is essential for ensuring your letters and packages reach their destinations. Follow USPS's standard format, use ALL CAPS, drop the punctuation, and double-check the ZIP — and most of your delivery problems disappear.

Quick Reference Checklist:

• Use the standard format: NAME / STREET ADDRESS / CITY STATE ZIP
• Include APT, STE, or UNIT numbers for multi-unit buildings
• Use two-letter state abbreviations (CA, NY, TX), never full names
• Double-check the ZIP code, and add ZIP+4 if you have it
• Write in ALL CAPS with no punctuation in the address block
• Include the destination country in capital letters for international mail

Or, skip the hassle entirely. Use PostPal and let our validated forms make sure your mail is addressed correctly every time. No more worrying about formatting, ZIPs, or legibility — just fill in the fields and we handle the rest. For more on US mail in general, see our guide on sending mail in the USA.

Send your first letter with PostPal today