Key findings
Across 338 US area codes, a total of 193,664 NXX central-office prefixes are assigned across 23431 rate centers — an average of ~72.3% of the ~792 usable prefixes per area code already in service. The most heavily assigned is 213 (Los Angeles) at 787 prefixes; 712 (Sioux City) shows the widest carrier diversity (115 carriers).
- Prefixes analyzed
- 193,664
- Area codes
- 338
- Rate centers
- 23431
- Avg. fill
- ~72.3%
An NXX is the three-digit central-office prefix that follows the area code in a North American Numbering Plan number (the NXX in NPA-NXX-XXXX). Each area code has roughly 792 usable NXX prefixes (the first digit runs 2–9). When a code's prefixes near exhaustion, regulators add an overlay. This page reports how many prefixes are actually assigned across 338 US area codes — every NANP geographic code with prefixes in service — a proprietary aggregation we maintain from public NANPA / localcallingguide records.
Assigned NXX prefixes by area code
| Area code | Primary metro | Assigned prefixes | Rate centers | Carriers | % of ~792 used |
|---|---|---|---|---|---|
| 213 | Los Angeles, CA | 787 | 16 | 52 | 99.4% |
| 330 | Akron, OH | 787 | 117 | 41 | 99.4% |
| 408 | San Jose, CA | 787 | 13 | 40 | 99.4% |
| 540 | Roanoke, VA | 787 | 117 | 59 | 99.4% |
| 619 | San Diego, CA | 787 | 17 | 46 | 99.4% |
| 847 | Evanston, IL | 787 | 50 | 34 | 99.4% |
| 217 | Springfield, IL | 786 | 265 | 60 | 99.2% |
| 267 | Philadelphia, PA | 786 | 36 | 48 | 99.2% |
| 301 | Rockville, MD | 786 | 64 | 40 | 99.2% |
| 310 | Los Angeles, CA | 786 | 18 | 38 | 99.2% |
| 323 | Los Angeles, CA | 786 | 12 | 41 | 99.2% |
| 360 | Olympia, WA | 786 | 75 | 65 | 99.2% |
| 410 | Baltimore, MD | 786 | 103 | 39 | 99.2% |
| 443 | Baltimore, MD | 786 | 81 | 40 | 99.2% |
| 469 | Dallas, TX | 786 | 53 | 57 | 99.2% |
| 470 | Atlanta, GA | 786 | 41 | 52 | 99.2% |
| 484 | Allentown, PA | 786 | 79 | 51 | 99.2% |
| 510 | Oakland, CA | 786 | 13 | 40 | 99.2% |
| 573 | Columbia, MO | 786 | 217 | 58 | 99.2% |
| 608 | Madison, WI | 786 | 159 | 81 | 99.2% |
| 618 | East St. Louis, IL | 786 | 243 | 63 | 99.2% |
| 702 | Las Vegas, NV | 786 | 16 | 45 | 99.2% |
| 713 | Houston, TX | 786 | 19 | 39 | 99.2% |
| 714 | Anaheim, CA | 786 | 15 | 40 | 99.2% |
| 720 | Denver, CO | 786 | 12 | 55 | 99.2% |
| 740 | Newark, OH | 786 | 187 | 50 | 99.2% |
| 757 | Norfolk, VA | 786 | 34 | 41 | 99.2% |
| 760 | Palm Springs, CA | 786 | 85 | 55 | 99.2% |
| 786 | Miami, FL | 786 | 5 | 54 | 99.2% |
| 804 | Richmond, VA | 786 | 55 | 45 | 99.2% |
| 805 | Oxnard, CA | 786 | 41 | 56 | 99.2% |
| 815 | Rockford, IL | 786 | 203 | 65 | 99.2% |
| 832 | Houston, TX | 786 | 46 | 45 | 99.2% |
| 909 | San Bernardino, CA | 786 | 25 | 51 | 99.2% |
| 916 | Sacramento, CA | 786 | 17 | 49 | 99.2% |
| 972 | Dallas, TX | 786 | 72 | 50 | 99.2% |
| 202 | Washington, DC | 785 | 1 | 39 | 99.1% |
| 208 | Boise, ID | 785 | 146 | 76 | 99.1% |
| 212 | New York City, NY | 785 | 1 | 29 | 99.1% |
| 215 | Philadelphia, PA | 785 | 36 | 39 | 99.1% |
| 240 | Rockville, MD | 785 | 63 | 50 | 99.1% |
| 281 | Houston, TX | 785 | 62 | 45 | 99.1% |
| 303 | Denver, CO | 785 | 13 | 39 | 99.1% |
| 317 | Indianapolis, IN | 785 | 36 | 41 | 99.1% |
| 407 | Orlando, FL | 785 | 17 | 48 | 99.1% |
| 415 | San Francisco, CA | 785 | 14 | 45 | 99.1% |
| 707 | Santa Rosa, CA | 785 | 75 | 50 | 99.1% |
| 773 | Chicago, IL | 785 | 27 | 37 | 99.1% |
| 803 | Columbia, SC | 785 | 83 | 60 | 99.1% |
| 816 | Kansas City, MO | 785 | 111 | 56 | 99.1% |
Showing the 50 most heavily assigned of 338 US area codes analyzed. Source: DialPhone aggregation of public NANPA / localcallingguide prefix records, 2026-06-18.
What the data shows
The most heavily assigned codes sit just under the ~792-prefix ceiling — 213 (Los Angeles) leads at 787 assigned prefixes. Saturation like this is why dense metros run multiple overlay codes: when a code nears prefix exhaustion, a new code is layered over the same geography rather than splitting it. Newer or rural codes sit far lower, which is why assignment counts span 13–787 across the set.
Rate-center spread varies widely: dense single-rate-center codes such as Los Angeles (213) concentrate all prefixes in one billing center, while Fargo (701) spreads its prefixes across 300 rate centers. Carrier diversity (how many carriers hold blocks) ranges from 9 to 115 carriers per code — a proxy for how competitive number provisioning is in each market.
Why it matters for getting a local number
Prefix saturation is why availability of a specific local business number varies by market: in heavily assigned codes, vanity and sequential numbers are scarcer and may sit in a different overlay code. DialPhone provisions local numbers across every active US and Canadian area code — see the full area-code directory for per-code detail.