Radon Risk Calculator
Enter a radon level of 0 or higher to see your result.
How this calculator works
The headline number comes straight from the U.S. EPA risk tables in A Citizen's Guide to Radon, which state how many people out of 1,000 are estimated to develop lung cancer over a lifetime of exposure at a given radon level. EPA publishes separate tables for people who have never smoked and for people who smoke or used to, because smoking and radon together are far more dangerous than either one alone.
EPA lists risk at specific levels (for example, 4 pCi/L and 8 pCi/L). For any number in between, this calculator draws a straight line between the two nearest EPA points and reads off the value, which is standard linear interpolation. Above 20 pCi/L the tool extends the same trend and flags the result as very high, because there is no published EPA point higher than 20 and the message at that point is simply to fix the home.
For the unit toggle, the conversion is exact: 1 pCi/L = 37 Bq/m3. So the EPA action level of 4.0 pCi/L is 148 Bq/m3, the WHO reference level of 100 Bq/m3 is about 2.7 pCi/L, and the Health Canada guideline of 200 Bq/m3 is about 5.4 pCi/L.
Reference levels vary by country, so this tool shows several. In Europe, the EU Basic Safety Standards Directive (2013/59/Euratom) requires each member state to set a national reference level for homes that does not exceed 300 Bq/m3 (about 8.1 pCi/L), and many countries use 300 Bq/m3 while some set it lower. The United Kingdom uses an Action Level of 200 Bq/m3 (about 5.4 pCi/L) and a lower Target Level of 100 Bq/m3. These are all annual-average figures, and the practical takeaway is the same everywhere: lower is better, and most homes above the local reference level can be fixed.
The key idea is that radon risk is a gradient, not an on or off switch. EPA is explicit that levels below 4 pCi/L still carry risk, and that no level is completely safe. The action levels and reference points are practical thresholds for deciding when to act, not a line between safe and dangerous.
About the cigarette comparison
The cigarette line is an approximate illustration, not a medical fact. It uses the long-standing EPA framing from A Citizen's Guide to Radon, where living at about 10 pCi/L was compared to smoking roughly 20 cigarettes a day, and living at 4 pCi/L to about 8 cigarettes a day. That works out to roughly 2 cigarettes a day for each 1 pCi/L, and we apply that simple ratio. Many radon programs and agencies have used this comparison to make the risk relatable. It has also been criticized, because smoking causes harm well beyond lung cancer and because radon and smoking interact, so treat the cigarette figure as a rough sense of scale rather than a precise equivalence. The EPA lifetime risk number above it is the more rigorous measure.
Sources
- U.S. EPA, A Citizen's Guide to Radon: The Guide to Protecting Yourself and Your Family from Radon (EPA 402/K-12/002), including the lifetime lung cancer risk tables for smokers and never-smokers, the 4 pCi/L action level, and the statement that no level of radon is completely safe.
- U.S. EPA, Health Risk of Radon and the Assessment of Risks from Radon in Homes (EPA 402-R-03-003), the underlying risk assessment behind the tables.
- U.S. EPA, 1986, original A Citizen's Guide to Radon, source of the cigarette comparison (about 20 cigarettes a day at roughly 10 pCi/L).
- World Health Organization, WHO Handbook on Indoor Radon, which proposes a reference level of 100 Bq/m3 (about 2.7 pCi/L) and up to 300 Bq/m3 where that is not feasible.
- Health Canada, the Canadian guideline of 200 Bq/m3 (about 5.4 pCi/L) for indoor radon in dwellings.
- European Union, the Basic Safety Standards Directive (Council Directive 2013/59/Euratom), which requires national reference levels for indoor radon in homes not exceeding 300 Bq/m3 (about 8.1 pCi/L) as an annual average.
- United Kingdom, the UK Health Security Agency (UKHSA, formerly Public Health England) Action Level of 200 Bq/m3 (about 5.4 pCi/L) and Target Level of 100 Bq/m3.
Frequently asked questions
What radon level is safe?
There is no level EPA calls completely safe. Risk falls as the level drops, so lower is always better. EPA recommends fixing your home at 4.0 pCi/L or higher and says to consider fixing it between 2 and 4 pCi/L. Even the average outdoor level of about 0.4 pCi/L carries a small risk.
Is the calculator a diagnosis or a prediction for me?
No. It reports EPA estimates for groups of 1,000 people exposed over a lifetime. Your personal risk depends on your actual exposure over time, your smoking history, genetics, and other factors. Use it to understand scale and decide whether to act, then test your home and talk to a professional.
My number is between the EPA values. Is the result still valid?
Yes. The tool interpolates between the nearest published EPA points, which is the standard way to read a value that falls between table entries. Results are rounded estimates, not exact counts.
What if my level is very high, above 20 pCi/L?
The risk is very high and the guidance is simple: fix it promptly with a qualified radon mitigation professional, then retest to confirm the level came down. The calculator extends the EPA trend above 20 and flags it as very high.
Don't know your number yet?
A test is the only way to find out. Start there, then come back and run your result.
See the best radon test kits →Related reading: What is radon and is it dangerous?, how to test your home for radon, the best radon test kits, and what radon mitigation costs.