Radon Levels
Radon test result interpreter
Short answer
Enter your radon result in pCi/L or Bq/m3 to see what it means under EPA's guidance and what to do next. EPA recommends fixing a home at 4 pCi/L (148 Bq/m3) or more on a long-term test or the average of two short-term tests, and considering a fix between 2 and 4 pCi/L.
Interpreter
Read your result
Type the number from your test report and choose its unit. Adding the kind of test and whether it was taken before or after a mitigation system makes the next step more specific. The tool restates EPA's testing guidance for that number; it does not diagnose anything or estimate a person's health risk.
The ranges
What each range means
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- Below 2 pCi/L (below 74 Bq/m³)Below both of EPA's guidance levels.
- 2 to 4 pCi/L (74 Bq/m³ to 148 Bq/m³)EPA recommends considering a fix when the level is between 2 and 4 pCi/L.
- At or above 4 pCi/L (148 Bq/m³ and up)EPA recommends fixing a home when the radon level is 4 pCi/L or higher.
- 4 pCi/L or more: EPA recommends fixing the home, once a long-term test or the average of two short-term tests confirms it. A single short-term result this high calls for a follow-up test first.
- 2 to 4 pCi/L: EPA recommends considering a fix. The average indoor level is 1.3 pCi/L, so a result in this range is above average.
- Below 2 pCi/L: no fix is called for, but radon varies, so you may want to test again sometime, and always after major renovations or if you start living on a lower floor.
Your test
How the kind of test changes the next step
| Your test | What the result tells you | Next step |
|---|---|---|
| One short-term test | A snapshot: less likely to show your year-round average | Follow up with a long-term test, or a second short-term test if you need an answer soon |
| Short-term result over 8 pCi/L | More than twice the action level | Take a second short-term test right away |
| Two short-term tests | Their average is the number to use | Fix the home if the average is 4 pCi/L or more |
| One long-term test | Closer to your year-round average | Fix the home if it is 4 pCi/L or more |
| Continuous monitor in a sale | An average over at least 48 hours | Fix the home if the average is 4 pCi/L or more |
One short-term test
- What the result tells you
- A snapshot: less likely to show your year-round average
- Next step
- Follow up with a long-term test, or a second short-term test if you need an answer soon
Short-term result over 8 pCi/L
- What the result tells you
- More than twice the action level
- Next step
- Take a second short-term test right away
Two short-term tests
- What the result tells you
- Their average is the number to use
- Next step
- Fix the home if the average is 4 pCi/L or more
One long-term test
- What the result tells you
- Closer to your year-round average
- Next step
- Fix the home if it is 4 pCi/L or more
Continuous monitor in a sale
- What the result tells you
- An average over at least 48 hours
- Next step
- Fix the home if the average is 4 pCi/L or more
The higher a short-term result, the more certain you can be that the home needs fixing. Not sure which test to run next? The test chooser picks one for your situation.
After a fix
Reading a result after mitigation
A test after installation shows whether the system works. Run it within 30 days of installation, but no sooner than 24 hours after the system starts running with the fan on, for two to seven days. An independent follow-up measurement is recommended as well: having an independent tester do it, or doing it yourself, removes any conflict of interest with the installer.
Units
pCi/L and Bq/m3: converting your number
× 37
pCi/L to Bq/m3: multiply by 37, or divide Bq/m3 by 37 to go back. Calculated by Radon411 from EPA's own pair, 4 pCi/L = 148 Bq/m3.
U.S. test reports use picocuries per liter (pCi/L). Many monitors and most other countries use becquerels per cubic meter (Bq/m3). EPA's action level of 4 pCi/L is 148 Bq/m3, and the average indoor level of 1.3 pCi/L is 48.1 Bq/m3. The World Health Organization recommends a reference level of 100 Bq/m3 for homes, about 2.7 pCi/L (calculated), so a result under 4 pCi/L can still be above it.
Fluctuation
Why one result can differ from the next
Radon levels tend to vary from day to day and season to season, so two tests rarely match. Opening windows, doors and lower-floor vents lowers the level for a while, and once they are closed it most often returns within about 12 hours, which is why tests run with the house closed.
FAQ
Radon result questions
What is a normal radon level?
The average indoor level is about 1.3 pCi/L (48.1 Bq/m3). EPA recommends considering a fix between 2 and 4 pCi/L and fixing at 4 pCi/L or more.
Is 4 pCi/L dangerous?
It is EPA's action level: EPA recommends fixing a home at 4 pCi/L or more on a long-term test or the average of two short-term tests.
What should I do if my result is between 2 and 4 pCi/L?
EPA recommends considering a fix. A long-term test gives a better picture of your year-round average before you decide.
My short-term test is high. Should I fix the house now?
Follow up first: a long-term test, or a second short-term test if you need an answer soon. If the first result is more than twice 4 pCi/L, take the second test right away.
How do I convert Bq/m3 to pCi/L?
Divide by 37 (calculated from EPA's pair, 148 Bq/m3 = 4 pCi/L). For example, 100 Bq/m3 is about 2.7 pCi/L.
Why did my second test read differently?
Radon varies from day to day and season to season, and opening the house changes it for hours. Read an average, and use a long-term test for your year-round level.
What result should I expect after mitigation?
Below 4 pCi/L. Test within 30 days of installation, no sooner than 24 hours after the system starts, and retest at least every two years.
Should I test again if my result is low?
You may want to test again sometime, and always after major renovations or if you start living on a lower floor of the home.