What does my radon test result mean?
Fix your home if radon is 4 pCi/L or higher, and consider fixing it between 2 and 4 pCi/L. Those are EPA's recommendations (EPA). If your first short-term test is 4 pCi/L or higher, run a second test before you decide, because radon levels change from day to day.
Key facts
- EPA action level: 4 pCi/L (150 Bq/m³). Consider fixing between 2 and 4 pCi/L (EPA).
- The World Health Organization's reference level is 100 Bq/m³, about 2.7 pCi/L (WHO).
- The average U.S. home is about 1.3 pCi/L; outdoor air is about 0.4 pCi/L (EPA).
- About 1 in 4 Tennessee homes that request a free state kit test above 4 pCi/L (Tennessee Radon Program).
What should I do with my result?
| Your result | What to do |
|---|---|
| Below 2 pCi/L | No action needed. Retest if you start using a lower floor or after major renovations. |
| 2 to 4 pCi/L | Consider fixing your home. No level is completely risk-free. |
| 4 pCi/L or higher, first short-term test | Run a second test to confirm before deciding. |
| 4 pCi/L or higher, average of two short-term tests, or any long-term test | Fix your home. Contact a certified mitigation professional. |
Source: CDC – Testing for Radon.
Is 4 pCi/L a safe level?
No. 4 pCi/L is the level at which EPA recommends fixing a home, not a line between safe and unsafe. Risk rises with the level and with years of exposure. At a lifetime exposure of 4 pCi/L, EPA estimates about 7 in 1,000 people who never smoked could get lung cancer, and about 62 in 1,000 smokers (EPA). That's why EPA recommends considering a fix between 2 and 4 pCi/L.
Why should I confirm a high short-term result?
A short-term test is a snapshot. Radon rises and falls with weather, season and how the house is used, so one test can read high or low. CDC advises confirming a short-term result of 4 pCi/L or higher with a second short-term test, or a long-term test, before you fix the home (CDC). If a long-term test reads 4 pCi/L or higher, you don't need to confirm it.
How do pCi/L and Bq/m³ compare?
U.S. results are reported in picocuries per liter of air (pCi/L). Most other countries use becquerels per cubic meter (Bq/m³). 1 pCi/L equals 37 Bq/m³ (EPA).
| pCi/L | Bq/m³ | What it is |
|---|---|---|
| 0.4 | about 15 | Average outdoor air (U.S.) |
| 1.3 | about 48 | Average U.S. home |
| 2.0 | 74 | Low end of EPA's "consider fixing" range |
| 2.7 | 100 | WHO reference level |
| 4.0 | 148 | EPA action level |
| 8.1 | 300 | WHO upper limit where 100 Bq/m³ can't be met |
My result is high. What happens next?
- Don't panic. Radon risk comes from years of exposure, so a few weeks to arrange a fix doesn't meaningfully change it.
- Confirm the result if it came from a single short-term test.
- Get quotes from certified professionals. Tennessee doesn't license radon mitigators, so look for NRPP or NRSB certification. See how to choose a radon professional.
- Retest after the system is installed, then at least every 2 years. See how radon mitigation works.
When should I test again?
Retest a few months after a radon reduction system is installed, and every 2 years after that (American Lung Association). Also retest after major renovations or before turning a basement or lower floor into living space (CDC). The free state kit works for these follow-up tests.
Frequently asked questions
My neighbor's result was low. Does that mean mine is too? No. Levels can differ a lot between neighboring homes because of the soil beneath each house and how it was built. Only a test of your home tells you its level.
Can I get a result of zero? Rarely. Outdoor air itself averages about 0.4 pCi/L, and EPA notes that getting indoor levels below 2 pCi/L can be difficult.
Who can help me understand my result? Call the Tennessee Radon Program at 1-800-232-1139, or the National Radon Helpline at 1-800-557-2366.
Next step: Find a certified radon professional →
Sources: EPA – Health Risk of Radon · CDC – Testing for Radon · WHO – Radon fact sheet · American Lung Association – Radon · Tennessee Radon Program
Last reviewed October 17, 2026 by the Tennessee Radon Authority editorial team. How we research.