ZIP+4 Code Format Guide: How to Use 9-Digit ZIP Codes
The ZIP+4 add-on can speed automated sorting and improve accuracy. Here's how the format works, when it helps, and where to look it up. For automated addressing and mailing, our online letter service handles ZIP+4 formatting automatically.
What is a ZIP+4 Code?
A ZIP+4 code is the 5-digit ZIP plus a 4-digit add-on that narrows delivery to a sector/segment within the ZIP. It supports USPS automation and routing but is not required for most mail.
ZIP+4 Format
Five digits, hyphen, four digits. Use the hyphen when writing the full 9-digit code.
Benefits of Using ZIP+4
- Improves automated sorting and routing
- Reduces misdelivery risk in high-density addresses
- Can speed processing for business/volume mail - use our bulk mailing service for automatic ZIP+4 formatting
- Our online mailing service handles ZIP+4 codes automatically
How to Find ZIP+4 Codes
Official USPS Lookup
Enter a full street address (including unit/floor if applicable) to get the precise ZIP+4.
Note: the tool returns addresses in USPS-standardized format.
Check Existing Mail
Statements and government or business mail often include your full ZIP+4.
Proper ZIP+4 Formatting (USPS Style)
✅ Correct
- Uppercase city/state line; two-letter state
- Hyphen between ZIP and +4; no spaces around the hyphen
Based on USPS Publication 28 addressing standards.
❌ Incorrect
- Mixed case and punctuation on last line
- Missing hyphen in ZIP+4
When to Use ZIP+4
- High-density delivery points (apartments, offices, campuses)
- Business/volume mail where automation matters
- Time-sensitive or important correspondence
ZIP+4 vs 5-Digit ZIP
| Feature | 5-Digit ZIP | ZIP+4 |
|---|---|---|
| Precision | General area | Specific sector/segment |
| Processing | Standard | Better automation |
| Required? | Yes (use at least 5 digits) | Optional but recommended |