How to Address an Envelope, and Where the Three-Line Rule Came From

Write the recipient's name on the first line, the full street address on the second with the apartment or suite number at the end of that same line, and the city, two-letter state abbreviation and ZIP Code on the third. Put that block in the lower center of the envelope, your return address in the upper left corner, and the stamp in the upper right. Those three bottom lines are the only ones the Postal Service uses to route the letter, so nothing goes below them and an apartment number never gets a line of its own after the city.

The three lines you were taught are the bottom three of eleven

Publication 28, the USPS Postal Addressing Standards, treats three lines as the floor rather than the format. Its section 341 lays out an address block of eleven numbered lines: an optional endorsement line, key line data, a barcode, a mailstop code, an attention line, an individual title, a functional title, a department name, a firm name, the delivery address line, and the city-state-ZIP line.

Section 343.1 is the part worth memorizing. "Lines #9, #10, and #11 contain addressing data elements that are required for distribution and delivery by the Postal Service. Therefore, they must appear as the last three lines of the address block." Lines 4 through 8 the standard calls optional outright. The three lines everyone draws are 9, 10 and 11 with the courtesy lines stripped off.

Their shape came from a machine. The USPS Historian's record of state abbreviations notes that when the five-digit ZIP Code launched on July 1, 1963, "most addressing equipment could accommodate only 23 characters (including spaces) in the bottom line of the address." Twenty-three characters had to hold a city, a state and a new five-digit number, and it was the state name that gave way. A June list went out, but many of its entries ran three or four letters, still too long; in October the Department settled on two. Only one has changed since, Nebraska moving from NB to NE in 1969 at the Canadian post's request.

Before all that, the Post Office preferred state names spelled out in full, to avoid confusion. NY and CA are not a house style. They are a character budget from 1963, still printed on every envelope in the country.

Name the destination type before you copy any diagram

The block changes with the destination, so decide which you have first:

• A street address with no unit.
• A street address with an apartment, suite, floor, room or lot.
• A PO Box, where the box number replaces the street.
• A rural route or highway contract route, in Publication 28 sections 24 and 25.
• An APO, FPO or DPO military or diplomatic address.
• An address in another country.

The standard three-line picture is correct for exactly one of those six. That is what makes a good diagram dangerous: it is accurate, and it looks universal.

The domestic block, line by line

``` MS ALICE FUENTES 4021 GLENWOOD AVE APT 3B RALEIGH NC 27612-3891 ```

Publication 28 section 212 asks for a uniform left margin and prefers uppercase, though legible lowercase is accepted. Section 231 breaks the delivery address line into seven components separated by single spaces: primary address number, predirectional, street name, suffix, postdirectional, secondary address identifier, secondary address. The Postal Service parses that line from the right-hand element leftward, so a stray element added after the secondary address is the first thing that parsing meets.

For the last line, section 224 requires at least one space between the city name, the two-character state abbreviation and the ZIP+4 Code, with two spaces preferred before the code. That last line is a routing field, not a flourish. Drop the city or state because the ZIP "already says it" and a single mistyped digit has nothing left to contradict it.

The ZIP+4 arrived in 1983 and, in the words of the Postal Service's own history, "added a hyphen and four digits to the existing five-digit ZIP Code." The sixth and seventh mark a delivery sector; the last two a delivery segment, described in that history as one floor of an office building or one side of a block. Section 343.1 says never to drop the hyphen. Take the four digits from the USPS ZIP Code Lookup or the recipient, never from a neighbour's address, since the segment is precisely what differs.

Where the apartment number goes, and where it does not

Section 213 is unambiguous. "Secondary address unit designators, such as APARTMENT or SUITE, are required to be printed on the mailpiece for address locations containing secondary unit designators. The preferred location is at the end of the Delivery Address Line."

There is one permitted alternative, and it goes upward. Sections 213.3 and 343.1 both say that when the information will not fit on the delivery address line, the secondary components belong on the line immediately above it:

``` APT 3B 4021 GLENWOOD AVE RALEIGH NC 27612-3891 ```

What the standard never offers is a line below the city. People write it there because that is how we say an address aloud, adding the apartment as an afterthought. There is no line 12 to receive it.

The geometry backs this up. Domestic Mail Manual 102.2.1 puts the optical character reader read area half an inch in from the left and right edges, running from 5/8 inch to 2-3/4 inches above the bottom edge. An extra line under the city either falls beneath that window or shoves the routing lines above it.

Appendix C2 of Publication 28 lists 24 approved designator abbreviations. Fifteen require a number to follow, including APT, STE, RM, FL and UNIT. Nine take no number at all: BSMT, FRNT, LBBY, LOWR, OFC, PH, REAR, SIDE, UPPR. Those nine I learned from a truck rather than a book; on a split house with two tanks and one street number, REAR and UPPR are the whole address, and guessing wrong fills the wrong tank. The pound sign is a last resort. Section 213 says not to use it when the correct designator is known, 213.2 wants a space between sign and number, and Appendix C2 requires it in one case only: the row labelled "Blank, unable to determine."

The return address, the stamp, and the envelope itself

USPS puts the return address in the top left corner, the delivery address in the bottom center, and the stamp in the upper right. Reversing the first two comes from copying a picture without noticing which corner belongs to the sender. The corner is yours. The center is theirs.

Domestic Mail Manual 102.4.2 adds that a return address at a multiple delivery address "must show a unit designator (e.g., an apartment number)." Your own unit number belongs there too, or a returned letter stalls in your lobby.

The envelope has limits of its own, in Domestic Mail Manual 101.1.1. A letter must be at least 5 inches long, 3-1/2 inches high and 0.007 inch thick, and no more than 11-1/2 inches long, 6-1/8 inches high and 1/4 inch thick, weighing no more than 3.5 ounces; above that it pays flat-size prices. Section 101.1.2 adds the machinability rules, and the one that catches people planning a wedding is the aspect ratio: length divided by height must fall between 1.3 and 2.5. A square invitation envelope has a ratio of 1.0, nonmachinable by definition. Clasps, strings and buttons do the same, as does an address written parallel to the shorter side.

Under Notice 123, the USPS price list effective July 12, 2026, a stamped First-Class letter costs $0.82 for the first ounce, a metered one $0.78, a postcard $0.65, and the nonmachinable surcharge adds $0.49. Prices move; check the current notice rather than this paragraph a year from now. Weigh and measure before buying stamps, not after sealing thirty invitations.

Whose name goes on the envelope

The name line does not route anything. Lines 9, 10 and 11 do that work, which is why a misspelled first name usually still arrives and a missing unit designator often does not.

For a business, Publication 28 section 214 places the attention line above the recipient line, meaning above the company name. For a household card, "The Ortega Family" over a correct address block is fine; the sorting equipment is indifferent to it.

Invitations are stricter, and there the authority is etiquette rather than the Postal Service. The Emily Post Institute treats "The [Surname] Family" as an invitation to every member of that household, so use it only when you mean everyone. In the traditional two-envelope set, the outer envelope carries formal names and the inner one names exactly who is invited, with children listed below their parents. That is how the omission does its work.

An international address and an APO/FPO address are opposites

Both feel like "mail going overseas," and their rules point in opposite directions on the last line.

| | Domestic US | International | APO / FPO / DPO | |---|---|---|---| | Last line | City, two-letter state, ZIP or ZIP+4 | Country name alone | APO/FPO/DPO, then AA/AE/AP, then 9-digit ZIP | | Country name | Not used | Required, in full, capitals, no abbreviation | Must not appear | | City name | Required | On the line above the country | Must not appear | | Postal code | On the last line | With the city line, not with the country | On the last line | | Lines | 11 available, 3 required | No more than five, if possible | 3 in the USPS examples | | Priced as | Domestic | International | Domestic |

The International Mail Manual, section 122.1, is explicit: "The last line of the address must show only the country name, written in full (no abbreviations) and in capital letters. If possible, the address should have no more than five lines." Appendix A3 of Publication 28 adds that foreign postal codes do not belong on that last line, and that the country name is not underlined. Canada is the standing exception, needing two spaces between province abbreviation and postal code: `OTTAWA ON K1A 0B1`.

Military mail inverts it. USPS instructs senders that "to prevent mail from entering foreign mail networks, do not include city or country names in APO/FPO/DPO shipping addresses." A letter to a base in Germany that helpfully says GERMANY can be handed to the German post instead of travelling through the military system at domestic prices. APO, FPO or DPO takes the city slot; AA, AE or AP takes the state slot. Section 225.1 assigns them: AE for Europe, the Middle East, Africa and Canada, AP for the Pacific, AA for the Americas excluding Canada. Section 238.1 allows five military types on the delivery address line, each with its number plus a box number: CPR, OPC, PSC, UPR or UNIT. A USPS example:

``` PFC JOHN DOE PSC 3 BOX 4120 APO AE 09021 ```

Check it before you seal it

1. Confirm the destination type: street, box, route, military or foreign.
2. Run the address through the USPS ZIP Code Lookup for the standardized form and the ZIP+4. Never guess a code from a nearby address.
3. Check that the unit designator sits at the end of the delivery address line, or directly above it.
4. Measure against the 5-by-3-1/2 minimum and the 11-1/2-by-6-1/8 maximum, and weigh against 3.5 ounces.
5. Read the block back under decent light. The International Mail Manual requires ink or type and rejects pencil, and a grey afternoon at a kitchen table produces handwriting a scanner reads differently than you do.

A returned letter is rarely a mystery. It is almost always a line in the wrong place, and the wrong place is almost always below the city.

Frequently asked questions

What is the correct way to address an envelope?

Three lines in the lower center of the envelope: the recipient's name, then the full street address with any apartment or suite number at the end of that line, then the city, two-letter state abbreviation and ZIP Code. The return address goes upper left, the stamp upper right.

How do I write the address on an envelope?

Write it left-aligned, in ink, with a uniform left margin on every line. USPS prefers uppercase but accepts legible lowercase. Leave at least one space between city, state and ZIP, with two preferred before the ZIP. Keep the block in the lower-center area of the envelope face.

How do I address an envelope for a family?

Use "The Ortega Family" or "The Ortegas" on the name line above a correct address block; USPS routes by address, not by name. For invitations, the Emily Post Institute treats "The [Surname] Family" as inviting the whole household, so name individual guests when children are excluded.

What is the correct address format?

Recipient name on the top line, the delivery address line beneath it including the secondary unit designator, and the city, state and ZIP+4 on the last line. USPS Publication 28 requires those three to be the final three lines of the block, with nothing written below them.

How should I address an envelope to an apartment?

Put the designator and number at the end of the street line: 4021 GLENWOOD AVE APT 3B. If it does not fit, place APT 3B on the line immediately above the street line. Never after the city, state and ZIP, which sits outside the block USPS reads.

How does an APO/FPO address differ from an international address?

An international address ends with the destination country's name alone, in full capitals. An APO/FPO/DPO address must never show a city or country; it ends with APO, FPO or DPO, then AA, AE or AP, then a nine-digit ZIP. Military mail is also priced as domestic mail.