Free · EPA county data · Census ZIP matching
Is radon a risk where you live?
Radon is an invisible, odorless gas that seeps up from the ground. Enter your ZIP code to see your county’s EPA radon zone, then learn how to test.
EPA: test every home, whatever the zone. Fix at 4 pCi/L or higher; consider fixing between 2 and 4.
Predicted county average above 4 pCi/L
Predicted county average 2 to 4 pCi/L
Predicted county average below 2 pCi/L
Zone definitions from EPA’s Map of Radon Zones fact sheet. EPA: the map should not be used to decide whether an individual home needs testing.
U.S. lung cancer deaths a year that EPA attributes to radon, about 2,900 of them among people who never smoked.
EPAEPA’s action level. Fix your home at or above it; consider fixing between 2 and 4 pCi/L.
EPAAverage U.S. indoor radon level from EPA’s national survey, versus about 0.4 pCi/L outdoors.
EPATools
Look up, test, decide
Radon zone lookup by ZIP
Enter a ZIP code to see the county (or counties) it falls in and each county’s EPA radon zone, with the data source and date.
Open →Radon level calculator
Enter a test result in pCi/L or Bq/m³. See how it compares with the EPA action level, the WHO reference level, and the U.S. average.
Open →Radon follow-up test planner
Got a first test back? Answer three questions and get EPA’s recommended next step: retest, long-term test, or fix.
Open →Why test
Your zone is a hint. Your test is the answer.
Radon forms naturally when uranium in soil and rock breaks down. It seeps into houses through cracks, joints, sump pits, and gaps around pipes, and builds up indoors, usually most on the lowest level. EPA ranks it as the second leading cause of lung cancer in the United States.
EPA’s county zones, drawn in 1993 from indoor measurements, geology, aerial radioactivity, soil permeability, and foundation types, tell you how common high radon is likely to be nearby. But two houses on the same street can test very differently. That is why EPA says to test every home, whatever the zone, and to fix homes at 4 pCi/L or higher.
Start with how to test your home. When your result comes back, the level calculator and follow-up planner tell you what EPA recommends next.
Guides
Plain answers, sourced
What is radon, and how does it get into homes?
Radon is a radioactive gas from uranium in soil and rock. Here is where it comes from, how it enters a house, and why levels vary so much.
Read →Radon health risks: what the evidence says
Why EPA ranks radon as the second leading cause of lung cancer, how smoking multiplies the risk, and what the numbers do and do not mean.
Read →Radon in well water
How radon gets into private well water, why the main risk is breathing it after it escapes indoors, and how to test and treat.
Read →The EPA radon zone map, explained
What EPA's 1993 Map of Radon Zones measures, how the three zones were set, its limits, and how to use it well.
Read →Radon myths and facts
Common misconceptions about radon, from 'only old houses' to granite countertops, checked against EPA guidance.
Read →How to test your home for radon
Where to put a test kit, how long to leave it, closed-house conditions, and how to avoid the mistakes that spoil results.
Read →By state