Radon guide
What is a safe radon level?
No level is completely safe, but EPA draws two lines. At 4 pCi/L or higher, fix your home. Between 2 and 4 pCi/L, consider fixing it. Below 2 pCi/L, further reduction is usually hard to achieve.
Radon is measured in picocuries per liter of air (pCi/L). For scale, outdoor air carries about 0.4 pCi/L and the average American home about 1.3 pCi/L. Congress set a long-term goal that indoor air should match outdoor air, a target no current method can promise for every house.
Check your number
Nothing you enter leaves your browser. 1 pCi/L equals 37 Bq/m³, the unit used outside the US.
Where common results fall
| Level | What it is | EPA guidance |
|---|---|---|
| 0.4 pCi/L | Typical outdoor air | The long-term goal for indoor air |
| 1.3 pCi/L | Average US home | No action recommended, risk is not zero |
| 2 to 3.9 pCi/L | Above average | Consider fixing |
| 4 pCi/L and up | EPA action level | Fix the home |
What the risk looks like over a lifetime
EPA's estimate of how many people out of 1,000, exposed to a level for a lifetime, could get lung cancer from radon. Smoking multiplies the effect.
| Radon level | Never smoked | Smokers |
|---|---|---|
| 20 pCi/L | about 36 in 1,000 | about 260 in 1,000 |
| 10 pCi/L | about 18 in 1,000 | about 150 in 1,000 |
| 8 pCi/L | about 15 in 1,000 | about 120 in 1,000 |
| 4 pCi/L | about 7 in 1,000 | about 62 in 1,000 |
| 2 pCi/L | about 4 in 1,000 | about 32 in 1,000 |
| 1.3 pCi/L | about 2 in 1,000 | about 20 in 1,000 |
EPA's figures assume lifetime exposure. Former smokers fall between the two columns.
Is 1.5 or 3 pCi/L safe?
A result of 1.5 sits just above the national average and below both EPA lines, so EPA does not call for a fix. A result near 3 is in the range where EPA suggests you consider one; since most homes can be brought to 2 pCi/L or below, many owners in that range choose to act, especially if anyone in the home smokes.
Results near 4 deserve a second look. EPA notes that when two short-term tests average 4.1 pCi/L, there is roughly an even chance that the true year-round average is a little under or over 4. A long-term test of more than 90 days settles the question better than a quick retest.
Why the basement number is often higher
Radon comes up from the soil, so the lowest floor usually reads highest. EPA asks you to test the lowest level you use regularly. If your basement reads 5 and the bedrooms upstairs read 2, the basement result is the one that decides whether to fix, because any finished lower level can become someone's bedroom later.
Not tested yet? See how to test your home, or find your county's radon zone.
Sources: EPA, A Citizen's Guide to Radon (2016); EPA, Home Buyer's and Seller's Guide to Radon (2024). Updated October 2026.