ZIP Code 20851 — Rockville, MD
20851 is a standard (street delivery) ZIP code serving Rockville, Maryland, in Montgomery 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 20851 at a glance
| ZIP code | 20851 |
|---|---|
| Primary city | Rockville |
| State | Maryland (MD) |
| County | Montgomery FIPS 24031 |
| ZIP type | Standard (street delivery) |
| Time zone | America/New_York |
| Population | 14,946 |
| Coordinates | 39.077670, -77.120890 |
How ZIP+4 works in 20851
The four digits after the hyphen encode a delivery segment inside 20851. 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 20851 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.
Other ZIP codes in Rockville
Nearby ZIP codes
Showing the closest twelve. See every ZIP code within 25 miles of 20851.
| ZIP | City | Distance |
|---|---|---|
| 20852 | Rockville, MD | 1.8 mi |
| 20853 | Rockville, MD | 2.2 mi |
| 20896 | Garrett Park, MD | 3.2 mi |
| 20850 | Rockville, MD | 3.3 mi |
| 20906 | Silver Spring, MD | 3.6 mi |
| 20855 | Derwood, MD | 4.1 mi |
| 20895 | Kensington, MD | 4.2 mi |
| 20902 | Silver Spring, MD | 4.8 mi |
| 20814 | Bethesda, MD | 5.1 mi |
| 20880 | Washington Grove, MD | 5.2 mi |
| 20892 | Bethesda, MD | 5.4 mi |
| 20889 | Bethesda, MD | 5.5 mi |
Questions about 20851
What is the ZIP+4 code for 20851?
20851 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 20851, you need to look up a specific street address to get them.
What city is 20851?
20851 is assigned to Rockville, Maryland, in Montgomery 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.