Radon measurement guide
What does pCi/L stand for?
pCi/L means picocuries per liter. In the United States, it is the most common unit used to report the concentration of radon gas in indoor air.
What is a picocurie?
A curie is a unit used to describe radioactivity. A picocurie is one trillionth of a curie. When a radon report says 4 pCi/L, it means the test measured a radon concentration of about four picocuries in each liter of air during the measurement period.
What do common radon numbers mean?
EPA recommends fixing a home when the radon level is 4 pCi/L or higher and recommends considering radon reduction between 2 and 4 pCi/L. The 4 pCi/L level is an action guideline, not a line between completely safe and unsafe air.
A radon result also reflects the conditions and duration of that particular test. Weather, season, ventilation, heating and cooling, foundation conditions, and test placement can all influence a measurement.
pCi/L vs. Bq/m³
Some countries and reports use becquerels per cubic meter, written Bq/m³. EPA commonly uses rounded equivalents of about 4 pCi/L = 150 Bq/m³ and 2 pCi/L = 75 Bq/m³ for homeowner guidance.
What should you do with a radon result?
Start by checking how the test was performed and whether follow-up testing is appropriate. If the result is elevated, compare qualified mitigation options and arrange post-mitigation testing after work is completed.
See our full radon levels guide or learn how radon testing and measuring works.
Planning next steps
If you already have a test result, you can use our estimator for a planning range or search for local professionals.
Reviewed August 28, 2026. Educational information only.