Short-term kit
RA100 short-term liquid scintillation radon test kit
- Lab fee extra
Method: Liquid scintillation
In home: 48 to 96 hours
Locations and reports
Radon Levels in San Francisco County, California
EPA puts San Francisco County in Zone 2, its middle radon zone, and most reported tests there come back low, though 2.8% of 246 (2008 to 2017, laboratory totals) reached 4 pCi/L. Homes with elevated levels occur in all three zones, so only a test measures yours.
Data checked By Radon411Methodology
Share at 4+ pCi/L
2.8%
7.5 pts below CA
- San Francisco
- 2.8%
- California
- 10.3%
246 tests, 2008 to 2017
Median result
0.5pCi/L
Below action level
- San Francisco
- 0.5 pCi/L
- EPA
- 4.0 pCi/L
Midpoint of the tests, 2008 to 2017
Tests reported
246
13th of 33 by tests
- San Francisco
- 246
- Los Angeles
- 2,363
Reported to CDC before any fix, 2008 to 2017
EPA radon zone
Zone 2
Moderate potential
- 1
- Zone 2
- 3
1 highest, 3 lowest
EPA predicts 2 to 4 pCi/L indoors
Rank in California
29 of 33
Lowest quarter
- San Francisco
- 2.8%
- El Dorado
- 30.3%
By share, of 33 with 30+ tests
Read a result for San Francisco County
Starts at San Francisco County's median, 0.5 pCi/L
EPA’s own thresholds; the figures are the area’s, never this home’s.
EPA’s reading of 0.5 pCi/L
Below 2 pCi/L
- Under 20 to 1.9 pCi/L
- 2 to 4consider a fix
- 4 and aboveEPA says fix it
This result is below 2 pCi/L, the level at which EPA says a fix should be considered. San Francisco County's median reported result, 2008 to 2017.
The data
San Francisco County, At a glance
San Francisco County at a glance
Predicted: EPA radon zone
EPA Zone 2: moderate predicted potential
San Francisco County is a
USGS geologic potential: Moderate across 90% of the county's area
Predicted: EPA Map of Radon Zones
Measured: tests reported to CDC
Radon tests reported for San Francisco County, 2008 to 2017, laboratory
Under 2 pCi/L: 89%2 to 4 pCi/L: 8%4 pCi/L and above: 3%
Of 246 pre-mitigation tests reported to CDC, not homes in this area.
| Result band | Tests Measured | Share Measured |
|---|---|---|
| Under 2 pCi/L | 218 | 88.6% |
| 2 to 4 pCi/L | 21 | 8.5% |
| 4 pCi/L and above | 7 | 2.8% |
What these figures count
These are the 246 tests reported to CDC for San Francisco County over 2008 to 2017 (laboratory totals), many from homes being sold or already suspected of a problem: they describe the county's reported tests, not this house.
Measured: CDC tracking data. Figure above: 2008 to 2017, laboratory. Measured data period: 2005 to 2017 (every CDC figure on file).
San Francisco County, Compared
San Francisco County radon figures, compared
Calculated by Radon411Only 7 of 246 radon tests reported for San Francisco County over the 2008 to 2017 laboratory totals reached 4 pCi/L (2.8%). The median result, 0.5 pCi/L, sits below 2, well under EPA's 4 pCi/L action level, and the top reported result was 28.6 pCi/L.
Across 56 California counties pooled together, 10.3% of tests reached that level, so San Francisco County runs 7.5 points below its state. Against the national pool of 35.7%, the gap is 32.9 points lower. Its place in the state: 29th of 33 California counties with 30 or more tests for the same period.
The reported tests do not follow EPA's Zone 2 label for San Francisco County (predicted average between 2 and 4 pCi/L): 2.8% of them reached 4 pCi/L, fewer than that label suggests. San Mateo County, the one bordering county with a figure for the same period, reported 9.2%.
Below the action level, 218 tests (88.6%) came in under 2 pCi/L, against 76.8% statewide, and 21 tests (8.5%) fell between 2 and 4, against 12.9% statewide. USGS geology rates 90% of the county's land moderate radon potential.
CDC's ten-year totals for San Francisco County went from 254 tests (2005 to 2014) to 246 (2008 to 2017), the share going from 2.4% to 2.8%.
Pooled shares: Radon411's sum of CDC's county counts for one period.
San Francisco County, Geology
The ground under San Francisco County
PredictedUSGS's geologic map puts all of San Francisco County's mapped land in one class: moderate radon potential. 89.7% of it lies in the area the map calls Southern Coast Ranges, to which USGS gives a radon index of 9, in the moderate band (9 to 11).
| Area | The rock, in USGS's words | Potential | Radon index | Share of land |
|---|---|---|---|---|
| Southern Coast Ranges | Metamorphosed marine sedimentary rocks, ultramafic rocks, Triasic metamorphic rocks, Mesozoic granitic rocks, and a series of fault-bounded linear basins in which Teriary marine and continental sedimentary rocks were deposited. | Moderate | 9 | 89.7% |
Names, descriptions and indexes: U.S. Geological Survey, Geologic Radon Potential Map (2025). Shares: Radon411, from the map cut to the boundary.
San Francisco County beside the ground around it
Across California 0.1% of the land is rated high; none of San Francisco County's is. San Mateo County, the one county that borders it, has more moderate-potential ground: 98.5%.
The map rates the ground, not the air in any home.
Local help
San Francisco County, Local resources
Radon testing and mitigation in San Francisco County
- California Indoor Radon ProgramCalifornia Indoor Radon Program, run by California Department of Public Health, licenses or certifies radon professionals and offers free or discounted test kits, and answers questions about testing and mitigation in California.Visit the program’s page(opens in a new tab)
- Free and low-cost kitsThe program says:
Discounted test kits can be purchased through our partner laboratory, Alpha Energy, for $14.95.
- Compare kits
- Professionals in California4 professionals are listed in California.
What California's program says
- Phone
- 1-800-745-7236
- Radonprogram@cdph.ca.gov
- Licensing of radon professionals
The Radon Program certifies all radon service providers operating in California.
What it means
San Francisco County, Questions
Questions about radon in San Francisco County
Are radon levels high in San Francisco County?
Over the 2008 to 2017 laboratory totals, 2.8% of the radon tests reported to CDC for San Francisco County, California were at or above 4 pCi/L, and the median reported pre-mitigation result was 0.5 pCi/L. Of 33 California counties with 30 or more tests for the same period, 28 reported a higher share; pooled, the state comes to 10.3%.
Which counties border San Francisco County?
San Francisco County borders 1 county: San Mateo County.
Products
San Francisco County, Products
Testing a home in San Francisco County
In San Francisco County, 2.8% of 246 tests reported to CDC over the 2008 to 2017 laboratory totals reached 4 pCi/L, against 10.3% pooled across California. In Zone 2 a short-term kit (2 to 90 days) is the quick first check in San Francisco County; a long-term test tells the year-round average.
Test kits and monitors3
See every kit and monitor
Long-term kit
RL116 long-term radon test kit
- Lab fee extra
Method: Alpha track
In home: 90 days to 12 months
Monitor
lüft plug-in radon and indoor air quality monitor
- C-NRPP 2024/25: Approved
- Plug-in
- Wi-Fi, Bluetooth
- App only
First reading: Within 90 minutes
- See every kit and monitor Test kits and monitors
Test kits and monitors: 1 of 3
Best radon monitors for San Francisco County homes, compared
Explore
San Francisco County, Bordering counties
Counties bordering San Francisco County
Calculated by Radon411- Radon levels in San Mateo CountyEPA zone 2
9.2%at or above 4 pCi/L
Median 0.9 pCi/L · 468 tests · 6.4 points above San Francisco County
San Francisco County, Cities and towns
Cities and towns in San Francisco County
San Francisco County has been losing residents: from 875,139 in 2020 to 826,079 on July 1, 2025, a fall of 5.6% by the Census Bureau's estimates. Packed into its land, that is 17,608 people per square mile. San Francisco, its one incorporated place, has 826,079 residents, 100.0% of the total. CDC's 246 reported tests for 2008 to 2017 work out to 0.3 per 1,000 residents (2025 estimate), close to California's 0.2.
San Francisco is the one incorporated place here; CDC publishes no figure by town, so it reads San Francisco County's.
| Place | Residents | Since 2020 | Share of residents |
|---|---|---|---|
| San Francisco | 826,079 | −5.6% | 100.0% |
One incorporated place, as listed in the U.S. Census Bureau’s 2020 place reference files. Residents: U.S. Census Bureau population estimates for July 1, 2025 (Vintage 2025).
San Francisco County, Homes
Homes in San Francisco County
San Francisco County has 411,542 homes, and many share a building: 49% are in buildings of five or more, 18% are detached houses, against 57% across California. The homes are older than California's as a whole: half were built before 1945 (1976 for California), and 62% date from before 1960. Most occupied homes here are rented: owners live in 38% (California: 56%). A tenant can run a test; a fix is the landlord's to make.
| Homes | San Francisco County | California |
|---|---|---|
| Housing units | 411,542 | 14,532,683 |
| Detached houses | 18% | 57% |
| In buildings of 5 or more | 49% | 24% |
| Mobile homes | under 1% | 4% |
| Built before 1960 | 62% | 27% |
| Built since 2000 | 14% | 18% |
| Middle year built | 1945 | 1976 |
| Owner-occupied | 38% | 56% |
Census Bureau, American Community Survey, 2019 to 2023: estimates from a sample of homes, looser for a small place. Shares by Radon411.