Components
Address line 1 vs line 2
Address Line 1 is the street address: house or building number, street name, and directional. Address Line 2 is optional and holds anything that sits alongside the street address rather than replacing it, most often an apartment, suite, unit, or floor number. If there is no apartment or suite, Line 2 is left blank rather than filled with something else.
Checked September 10, 2026/5 min read
Written by Claire PostReviewed against USPS Publication 28
What is on this page6 sections
Most of the confusion around Address Line 1 and Address Line 2 is not about the rule itself, it is about the fact that two form fields turn into one line the moment the address ends up on an actual envelope. Once that mapping is clear, the fields are simple: Line 1 is the street, Line 2 is whatever rides along with it.
The most common mistake is not filling Line 2 in wrong, it is leaving an apartment or suite number off entirely because the form made it look optional in a way that suggested it did not matter. It does. A missing unit number in Line 2 is functionally the same problem as leaving it off an envelope street line altogether.
Step by step
Put the street address in Line 1
House or building number, street name, and any directional prefix or suffix. This is the core delivery information and always goes in the first field.
Use Line 2 only for something that rides alongside the street address
An apartment, suite, unit, floor, or building number. Line 2 exists to hold a second identifier at the same physical street address, not a second address.
Line 1: 512 W CHESTNUT STLine 2: APT 3CorrectA typical two-field form entry. Leave Line 2 blank if there is nothing that belongs there
A single-family house or a business with its own building has nothing to put on Line 2. An empty Line 2 field is correct and expected, not a sign something is missing.
Know what does not belong in Line 2
City, state, and ZIP have their own fields and never belong on Line 2. A c/o (care of) name also generally has its own line when the form supports it; if it does not, it goes on Line 2 rather than Line 1, since the street address itself still needs its own line.
Combine the two fields onto one line for a physical envelope
Line 1 and Line 2 are separate only because the form asks for them that way. On an actual envelope, they merge into a single street line, with the Line 2 content added to the end of the street address.
Quick reference
| Field | Holds | Example |
|---|---|---|
| Address Line 1 | Street number, street name, directional | 512 W CHESTNUT ST |
| Address Line 2 (optional) | Apartment, suite, unit, floor, building | APT 3 |
| City / State / ZIP | Separate fields, never part of Line 2 | BOISE, ID 83702 |
Special cases
The rule above covers most people. Here is what changes for the rest.
What if my apartment number will not fit alongside the street name in Line 1?
Put the street address in Line 1 as usual and the unit number in Line 2. The two-field split exists specifically to handle this case without cutting off part of the address — see <a href="/how-to-address-envelope-apartment/">addressing an envelope to an apartment</a> for the envelope version of this same placement rule.
Can I put a second street address, like a business suite in a different building, in Line 2?
No. Line 2 is for a second identifier at the same street address, not a separate location. If a recipient has two genuinely different addresses, that calls for two separate address entries, not one entry split across both fields.
Does it matter if I put "Apt 3" or just "3" in Line 2?
Include the designator (APT, STE, UNIT) rather than the number alone. Without it, "3" on its own line is easy to misread as unrelated to the street address at all.
Key terms on this page
- Address Line 1
- The form field holding the core street address: house or building number, street name, and directional.
- Address Line 2
- An optional form field for a secondary identifier at the same street address, most commonly an apartment, suite, unit, or floor number.
- Secondary address unit designator
- The abbreviation, like APT, STE, or UNIT, that identifies what kind of secondary identifier a number in Line 2 refers to.
