Updated November 2026 · Sources
Short answer: there is no known safe level of radon. The U.S. EPA recommends fixing your home if radon is 4 pCi/L or higher and considering a fix between 2 and 4 pCi/L. Canada’s guideline is 200 Bq/m³ (about 5.4 pCi/L), and the World Health Organization suggests a reference level of 100 Bq/m³ (about 2.7 pCi/L).
Radon levels and what to do
| Radon level | What it means | What to do |
|---|---|---|
| Below 2 pCi/L (below 74 Bq/m³) | Lower risk; reducing radon below 2 pCi/L is difficult | Retest in the future, and after major renovations |
| 2 to 4 pCi/L (74 to 148 Bq/m³) | Some risk; EPA says no level is safe | Consider fixing your home |
| 4 pCi/L or higher (148 Bq/m³ or more) | At or above the EPA action level | Confirm with a second test, then fix your home |
| Above 200 Bq/m³ (5.4 pCi/L) | Above the Canadian guideline | Health Canada: fix within one year |
Lifetime lung cancer risk by radon level
The EPA estimates how many people out of 1,000 could get lung cancer if exposed to a radon level over a lifetime:
| Radon level | Never smoked (per 1,000 people) | Smokers (per 1,000 people) |
|---|---|---|
| 20 pCi/L | About 36 | About 260 |
| 10 pCi/L | About 18 | About 150 |
| 8 pCi/L | About 15 | About 120 |
| 4 pCi/L | About 7 | About 62 |
| 2 pCi/L | About 4 | About 32 |
| 1.3 pCi/L (average indoor level) | About 2 | About 20 |
Radon is the second leading cause of lung cancer in the United States after smoking, and the EPA estimates it causes about 21,000 lung cancer deaths a year. Smoking and radon together raise the risk far more than either alone.
Converting pCi/L and Bq/m³
The U.S. uses picocuries per liter (pCi/L); Canada, Europe and the WHO use becquerels per cubic meter (Bq/m³). 1 pCi/L = 37 Bq/m³.
| pCi/L | Bq/m³ |
|---|---|
| 1.3 | 48 |
| 2 | 74 |
| 2.7 | 100 |
| 4 | 148 |
| 5.4 | 200 |
| 8.1 | 300 |
| 10 | 370 |
| 20 | 740 |
How common are high levels?
The EPA estimates that nearly 1 in 15 U.S. homes has an elevated radon level, but in some areas the share is far higher: in Pennsylvania DEP records, about a third of tests are at or above 4 pCi/L. See the results for your state.
Frequently asked questions
Is 4 pCi/L dangerous?
4 pCi/L is the level at which the EPA recommends fixing your home. The EPA estimates that about 7 in 1,000 people who never smoked, and about 62 in 1,000 smokers, could get lung cancer from a lifetime at that level.
Is 2 pCi/L safe?
The EPA says no level of radon is safe. At 2 pCi/L it recommends considering a fix, though reducing radon below 2 pCi/L is often difficult.
What is a normal radon level in a house?
The average U.S. indoor level is about 1.3 pCi/L, and outdoor air averages about 0.4 pCi/L, according to the EPA.
What is the radon limit in Canada?
Health Canada’s guideline is 200 Bq/m³ (about 5.4 pCi/L). Above that, it recommends fixing the home within one year.