Guides to US addresses and ZIP codes, page 21

Practical guides on address formats, ZIP codes, area codes and test data, plus reference pages for every state and major city.

Address basics
How to Format Apartment, Suite and Unit Numbers
Where apartment, suite, floor and unit numbers go in a US address, which abbreviations to use and how to handle long lines.
Address basics
How to Address Mail to the United States from Another Country
Formatting tips for sending letters and packages to US addresses from abroad, including the country line and ZIP code placement.
Testing and development
Address Normalization and Duplicate Detection
How to normalize US addresses before saving them, so duplicates are easy to find and data stays clean for shipping and reporting.
ZIP codes
What Is ZIP+4 and When Should You Use It?
ZIP+4 adds four digits to a five-digit ZIP code to pinpoint a delivery segment. Learn what the extra digits mean and when they help.
Phone numbers
US Area Codes and Phone Number Format Explained
How US phone numbers are structured, what area codes are, and why 555-0100 to 555-0199 numbers are safe for testing and fiction.
Address basics
How a US Mailing Address Is Structured, Line by Line
Learn the parts of a standard US mailing address: recipient, street line, secondary unit, city, state and ZIP code, with correct USPS order.
Responsible use
Why a Generated Address Should Never Be Used for Real Transactions
Generated addresses are for testing and learning. Here is why using one to sign up, order or verify identity can cause problems.
Address basics
PO Box vs Street Address: Key Differences
Compare PO Boxes and street addresses: how they are formatted, which carriers deliver to them and when businesses should accept each.
ZIP codes
How ZIP Codes Are Assigned: The First Three Digits Explained
The first digit of a ZIP code marks a group of states, and the first three mark a sectional center facility. Here is how the system works.
Testing and development
Using Generated Addresses for Software Testing: A Practical Guide
How QA teams and developers use realistic generated US addresses to test forms, databases, shipping logic and tax rules without real customer data.
Address basics
How to Write an Address on an Envelope
Where to place the delivery address, return address and stamp on a US envelope, with spacing tips that help automated sorting.
Address basics
USPS Street Suffix and Unit Abbreviations You Should Know
A practical reference for the USPS standard abbreviations for street suffixes like AVE and BLVD and unit designators like APT, STE and FL.
Geography
US Time Zones and How They Relate to Addresses
How the six main US time zones map to states and ZIP codes, which states are split between zones, and why it matters for apps.
Address basics
Military Addresses Explained: APO, FPO and DPO
How to write addresses for US military and diplomatic personnel overseas using APO, FPO, DPO and the AA, AE and AP state codes.
Testing and development
Why QA Teams Should Avoid Real Customer Data in Testing
Using production customer data in test environments creates privacy and security risks. Here is why generated test data is the safer choice.
Testing and development
Generating Bulk Test Addresses as CSV and JSON
How to create and use bulk US test addresses in CSV and JSON formats for database seeding, imports and automated tests.
Testing and development
Address Form Validation Rules for Web Developers
Practical validation rules for US address forms: required fields, ZIP code patterns, state lists, length limits and friendly error messages.
Address basics
US State Abbreviations: Complete List of Two-Letter Codes
The full list of USPS two-letter abbreviations for all 50 states and the District of Columbia, plus territory and military codes.
Address basics
Rural Route and Highway Contract Addresses
What rural route (RR) and highway contract (HC) addresses are, how to format them and why many have been converted to street addresses.
Testing and development
Designing Address Fields for a Better Checkout
UX guidelines for US address forms: field order, autocomplete attributes, labels, mobile keyboards and error handling that reduce drop-off.