Before you begin
What this tool needs
Use the EPA address-level map for more local context after this result.
Answer occupancy based on where people spend substantial time at ground level.
Reading the answer
What your result means
Every result leads to testing. The priority changes, not the need for a once-off measurement.
The national reference level for homes is 200 Bq/m³.
Boundaries
Assumptions and limitations
Working assumptions
- County groupings are deliberately broad and used only as one component of priority.
- Older construction, basement occupation and low ventilation raise the priority score, not the measured radon level.
Where to be careful
- Within-county variation is much larger than a county average.
- The result is not a radon measurement and cannot clear a house as safe.
Common questions
Questions about this tool
How is a home radon test done?
EPA guidance uses two small detectors, usually one in a bedroom and one in a living room, for at least three months.
Can a lower-risk area still contain a high-radon home?
Yes. High readings occur outside mapped high-radon areas, which is why a physical test is the only answer for a house.