Radon testing guide
How are radon levels measured?
Radon in indoor air is commonly measured in picocuries per liter (pCi/L) in the United States. A test measures the concentration of radon during a specific period, so the result should always be read together with the test type, duration, placement, and conditions.
Short-term radon measurement
Short-term tests are useful when a quicker result is needed. Depending on the device, they may run for a few days or longer. Because radon levels naturally fluctuate, a short-term result is a snapshot rather than a permanent reading for the home.
Long-term radon measurement
Long-term tests run for more than 90 days and can provide a better picture of average conditions across changing weather and seasons when there is no urgent deadline.
Why placement and test conditions matter
Device location, open windows or doors, ventilation, heating and cooling, weather, and whether required closed-house conditions were followed can all affect a result. Real-estate transactions may also have specific testing protocols or state requirements.
How to read the number
EPA recommends fixing a home at 4 pCi/L or higher and recommends considering reduction between 2 and 4 pCi/L. The action level is a decision benchmark, not a guarantee that readings below it carry no risk.
For more detail, read what pCi/L stands for and how to interpret radon levels.
What happens after an elevated result?
Follow appropriate confirmation guidance, compare qualified mitigation options, and retest after a mitigation system is installed to verify the result.
Reviewed August 28, 2026. Educational information only.