ZIP Code 94528 — Diablo, CA
94528 is a standard (street delivery) ZIP code serving Diablo, California, in Contra Costa County. To mail something here you only need these five digits — but the four-digit extension narrows delivery to a single point, and it is what USPS bulk postage discounts are priced on.
ZIP code 94528 at a glance
| ZIP code | 94528 |
|---|---|
| Primary city | Diablo |
| State | California (CA) |
| County | Contra Costa FIPS 06013 |
| ZIP type | Standard (street delivery) |
| Time zone | America/Los_Angeles |
| Population | 1,049 |
| Coordinates | 37.841490, -121.958190 |
How ZIP+4 works in 94528
The four digits after the hyphen encode a delivery segment inside 94528. In practice one segment usually means:
- One side of one block — odd numbers on a street between two cross streets
- A single large building, or one floor of it
- A group of PO boxes, sometimes a single box
- A single business that receives enough mail to warrant its own code
That is why 94528 has no single ZIP+4: two neighbors across the street from each other usually have different ones. Enter a street address above and we will return the exact nine-digit code along with the standardized USPS address format.
Nearby ZIP codes
Showing the closest twelve. See every ZIP code within 25 miles of 94528.
| ZIP | City | Distance |
|---|---|---|
| 94526 | Danville, CA | 2.3 mi |
| 94507 | Alamo, CA | 2.8 mi |
| 94506 | Danville, CA | 3.7 mi |
| 94598 | Walnut Creek, CA | 3.8 mi |
| 94583 | San Ramon, CA | 5.1 mi |
| 94596 | Walnut Creek, CA | 5.4 mi |
| 94517 | Clayton, CA | 5.4 mi |
| 94582 | San Ramon, CA | 5.9 mi |
| 94595 | Walnut Creek, CA | 6.4 mi |
| 94521 | Concord, CA | 7.7 mi |
| 94556 | Moraga, CA | 8 mi |
| 94597 | Walnut Creek, CA | 8.1 mi |
Questions about 94528
What is the ZIP+4 code for 94528?
94528 is the five-digit ZIP code. The ZIP+4 adds four more digits that identify a specific delivery point — usually one side of a city block, a single building, or a group of PO boxes. Because those four digits change from address to address within 94528, you need to look up a specific street address to get them.
What city is 94528?
94528 is assigned to Diablo, California, in Contra Costa County.
Do I need to use the ZIP+4?
It is optional for ordinary mail, but it speeds up sorting and it is required for most USPS bulk-mail postage discounts. Many address-verification and e-commerce systems also use ZIP+4 to confirm a delivery point exists.
Need thousands of these?
Upload a CSV and get ZIP+4, county, carrier route, and delivery-point data appended to every row — or call the API directly.