Radon level guide
What is the radon reference level?
A radon reference or action level is a benchmark used to guide decisions about follow-up testing or mitigation. In the United States, EPA recommends fixing a home at 4 pCi/L or higher and recommends considering reduction between 2 and 4 pCi/L.
Is 4 pCi/L a safe level?
No single radon number creates a sharp safe-versus-dangerous boundary. EPA uses 4 pCi/L as an action level for practical decision-making and notes that risk can still exist below that level.
Why do different organizations use different numbers?
Radon guidance can vary by country and agency because reference levels are policy benchmarks built around risk reduction, building practices, and public-health goals. When a state, transaction, or local program has a specific requirement, follow the current rule that applies to that situation.
What if your result is near 4 pCi/L?
Review the test type, duration, placement, and conditions. Depending on the situation, follow-up testing may help characterize the level more accurately. If the result supports mitigation, a property-specific system design and post-installation test are more useful than treating one number as a permanent label for the home.
Related radon guides
Read Radon Levels Explained, what pCi/L means, or what 4 pCi/L means for a homeowner.
Need to plan a mitigation project?
Use the estimator for a planning range or search for nearby radon professionals.
Reviewed August 28, 2026. Educational information only.