Radon level calculator

By the Radon by ZIP editorial team · Last reviewed September 29, 2026 · How we research

The two units

U.S. test kits and labs report radon in picocuries per liter of air (pCi/L). Most other countries, and the World Health Organization, use becquerels per cubic meter (Bq/m³). One pCi/L equals 37 Bq/m³, so EPA’s action level of 4 pCi/L is about 148 Bq/m³, which EPA rounds to 150. Some older reports and continuous monitors show “working levels” (WL), a measure used for radon decay products; if your report uses WL, ask the lab to convert it.

EPA’s numbers

EPA’s guidance is to fix your home if the radon level is 4 pCi/L or higher, and to consider fixing between 2 and 4 pCi/L. EPA also says there is no known safe level of radon exposure; the action level is where EPA judges that fixing is clearly worthwhile and achievable. According to EPA, a national residential survey completed in 1991 found an average indoor level of about 1.3 pCi/L and an average outdoor level of about 0.4 pCi/L.

The WHO reference level

In its 2009 Handbook on Indoor Radon, the World Health Organization proposed a national reference level of 100 Bq/m³ (about 2.7 pCi/L), and where that cannot be met, a level not exceeding 300 Bq/m³. EPA has said it keeps 4 pCi/L as its action level while encouraging people to consider fixing homes between 2 and 4 pCi/L. Your state may set its own guidance; the state programs linked on our state pages can tell you.

One test is a snapshot

Radon levels move with weather, season, and how the house is used. A short-term test (2 to 90 days) is a snapshot, and a long-term test (more than 90 days) is closer to your year-round average. If your first short-term result is 4 pCi/L or higher, EPA’s guidance is to follow up before deciding. Our follow-up test planner walks through those steps, and short-term vs long-term tests explains the difference.