The Bay Area here is the nine counties that border San Francisco Bay: Alameda, Contra Costa, Marin, Napa, San Francisco, San Mateo, Santa Clara, Solano and Sonoma. That is the usual nine-county definition. Wider definitions add other counties; they are not in this guide.
Verizon is the clear outdoor leader in 6 of the nine counties, and in 3 no carrier clearly leads once the county's water is allowed for, on the carriers' reported coverage as of December 31, 2025. In the 14 Bay Area cities among the 300 largest in the US, Verizon is the clear leader in 3 and 11 have no clear leader.
Several of these counties, and San Francisco above all, take in a lot of bay and ocean. The area figures count that water in each county, and carriers differ in whether they file coverage over it, so this guide names a leader only where the lead is bigger than the water could explain.
Every Bay Area county, outdoors
Each carrier's share of the county's area where it reports 4G LTE or 5G to a phone outdoors, the county's water share, and the outdoor leader under the site's water rule. Of 9 counties, Verizon leads in 6, AT&T leads in none and T-Mobile leads in none, and 3 have no clear leader.
| County | 4G, any carrier | AT&T | T-Mobile | Verizon | Water | Outdoor leader |
|---|---|---|---|---|---|---|
| Alameda County, CA | 90.2% | 69.9% | 67% | 88.7% | 10.2% | Verizon |
| Contra Costa County, CA | 98.2% | 87% | 84.3% | 97.3% | 10.8% | No clear leader on land (10.8% water) |
| Marin County, CA | 88.4% | 45.6% | 34.3% | 84.5% | 37.2% | Verizon (AT&T close behind) |
| Napa County, CA | 91.3% | 75% | 61.6% | 87% | 5.1% | Verizon |
| San Francisco County, CA | 82.6% | 20.3% | 20.3% | 82.6% | 79.9% | No clear leader on land (79.9% water) |
| San Mateo County, CA | 89.9% | 45.3% | 36.9% | 88.2% | 39.5% | Verizon (AT&T close behind) |
| Santa Clara County, CA | 83.5% | 61.1% | 51.7% | 80.5% | 1% | Verizon |
| Solano County, CA | 99.6% | 91.1% | 91.4% | 99.1% | 9.3% | No clear leader on land (9.3% water) |
| Sonoma County, CA | 86.1% | 61.9% | 54% | 80.8% | 10.9% | Verizon |
Shares of the county's total area, water included. A leader is named only when it is 5+ points ahead of the weakest carrier after allowing for the county's water. Share of area where each carrier reports 4G LTE or 5G to a phone outdoors, as of December 31, 2025. Reported coverage, not measured signal.
The largest Bay Area cities
The 14 Bay Area cities among the 300 largest in the US, biggest first. A city's figures cover the city itself, which is mostly built-up land, so they are a better guide to everyday coverage than the county rows.
| City | Population | AT&T | T-Mobile | Verizon | Water | Leader | |
|---|---|---|---|---|---|---|---|
| San Jose | 997,368 | 93.9% | 91.1% | 97.9% | 1.7% | Verizon (AT&T close behind) | View → |
| San Francisco | 827,526 | 20.3% | 20.3% | 82.6% | 79.9% | No clear leader on land (79.9% water) | View → |
| Oakland | 443,554 | 71.5% | 69% | 100% | 28.3% | No clear leader on land (28.3% water) | View → |
| Fremont | 228,192 | 79.9% | 87.4% | 100% | 11.5% | Verizon (T-Mobile close behind) | View → |
| Santa Rosa | 177,524 | 98.4% | 99.6% | 100% | 0.4% | Tie (within 5 points) | View → |
| Hayward | 158,440 | 60.3% | 65.2% | 99.9% | 28.5% | Verizon | View → |
| Sunnyvale | 156,792 | 96.3% | 96.5% | 100% | 3.2% | Tie (within 5 points) | View → |
| Santa Clara | 133,132 | 99.8% | 100% | 100% | 0% | Tie (within 5 points) | View → |
| Concord | 124,016 | 98.7% | 100% | 100% | 0% | Tie (within 5 points) | View → |
| Vallejo | 123,475 | 68.1% | 69.1% | 100% | 37% | No clear leader on land (37% water) | View → |
| Fairfield | 122,646 | 99% | 99.6% | 100% | 0.7% | Tie (within 5 points) | View → |
| Berkeley | 121,749 | 59.2% | 58.5% | 100% | 40.9% | No clear leader on land (40.9% water) | View → |
| Antioch | 118,453 | 98.2% | 99.6% | 100% | 2.6% | Tie (within 5 points) | View → |
| Richmond | 115,353 | 54.2% | 54.8% | 99.7% | 42.8% | No clear leader on land (42.8% water) | View → |
Population: 2024 estimates. Share of area where each carrier reports 4G LTE or 5G to a phone outdoors, as of December 31, 2025. Reported coverage, not measured signal.
Where the water hides the answer
In Contra Costa, San Francisco and Solano, the best-covered carrier files more of the county than the weakest, but the gap is not at least 5 points bigger than the county's water share. The table says there is no clear leader on land rather than crowning the carrier that files over the bay.
That is the same rule every page on this site uses.
Head to head
The same nine counties, one pair of carriers at a time. A county counts for a carrier only when its lead over the other beats the county's water share by 5 points.
Verizon vs AT&T: Verizon leads in 4, AT&T in 0, and 5 are too close to call.
Verizon vs T-Mobile: Verizon leads in 6, T-Mobile in 0, and 3 are too close to call.
AT&T vs T-Mobile: AT&T leads in 2, T-Mobile in 0, and 7 are too close to call.
| Matchup | First carrier leads | Second carrier leads | Too close to call |
|---|---|---|---|
| Verizon vs AT&T | 4 | 0 | 5 |
| Verizon vs T-Mobile | 6 | 0 | 3 |
| AT&T vs T-Mobile | 2 | 0 | 7 |
Outdoor figures, the nine Bay Area counties. Share of area where each carrier reports 4G LTE or 5G to a phone outdoors, as of December 31, 2025. Reported coverage, not measured signal.
In a moving car
Each carrier also reports a second map, for a phone in a moving vehicle, the one that matters on the freeway. Of 9 counties, Verizon leads in 7, AT&T leads in none and T-Mobile leads in none, and 2 have no clear in-car leader.
| County | AT&T, in a car | T-Mobile, in a car | Verizon, in a car | In-car leader |
|---|---|---|---|---|
| Alameda County, CA | 53.3% | 40.8% | 67.6% | Verizon (AT&T close behind) |
| Contra Costa County, CA | 67.9% | 53.1% | 78.5% | Verizon (AT&T close behind) |
| Marin County, CA | 23.8% | 14.4% | 47.6% | No clear leader on land (37.2% water) |
| Napa County, CA | 35.6% | 21.2% | 47% | Verizon |
| San Francisco County, CA | 20.2% | 17.7% | 58.5% | No clear leader on land (79.9% water) |
| San Mateo County, CA | 34.1% | 23.8% | 70.9% | Verizon (AT&T close behind) |
| Santa Clara County, CA | 43.5% | 31.1% | 49.4% | Verizon (AT&T close behind) |
| Solano County, CA | 57.7% | 44.9% | 73.5% | Verizon |
| Sonoma County, CA | 34.4% | 24.9% | 50.8% | Verizon |
Share of area where each carrier reports 4G LTE or 5G to a phone outdoors, as of December 31, 2025. Reported coverage, not measured signal.
5G in the Bay Area
All carriers combined, since the county 5G figures are not split by carrier. Shares of the county's total area, water included.
| County | 5G 7/1 Mbps | 5G 35/3 Mbps | 4G LTE, any carrier |
|---|---|---|---|
| Alameda County, CA | 80.4% | 70.9% | 90.2% |
| Contra Costa County, CA | 92.7% | 84.2% | 98.2% |
| Marin County, CA | 61.9% | 47.6% | 88.4% |
| Napa County, CA | 72.3% | 54% | 91.3% |
| San Francisco County, CA | 58.2% | 49.1% | 82.6% |
| San Mateo County, CA | 77% | 62.3% | 89.9% |
| Santa Clara County, CA | 65.6% | 50.4% | 83.5% |
| Solano County, CA | 96.4% | 80.1% | 99.6% |
| Sonoma County, CA | 70.9% | 60.1% | 86.1% |
Share of area where each carrier reports 4G LTE or 5G to a phone outdoors, as of December 31, 2025. Reported coverage, not measured signal.
Where to look next
A county or city figure is an average over a lot of ground, and in hilly country the signal at a house can differ from the map either way. For one address, use the carriers' own maps.