Radon Levels Chart: What Your pCi/L Test Result Means

2: consider fixing 4: fix

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For reference on the scale: the average US home measures about 1.3 pCi/L and outdoor air about 0.4 pCi/L (EPA). The reader keeps your number in this page only; nothing is sent anywhere.

Radon levels chart

EPA's lines are drawn at 2 and 4 pCi/L. The step depends on the number and on whether it came from a short-term or a long-term test.

Result	What EPA says	Next step	Source
Under 2 pCi/L	Below both EPA lines.	Even with a result under 4 pCi/L, EPA suggests testing again at some point in the future.	U.S. Environmental Protection Agency
2 to under 4 pCi/L	EPA also recommends that people consider fixing their home when the level is between 2 and 4 pCi/L.	EPA leaves the choice to you in this range; a long-term test shows the year-round level.	U.S. Environmental Protection Agency
4 to 8 pCi/L	EPA recommends fixing a home when the radon level is 4 pCi/L or more, which EPA writes as 150 Bq/m3.	EPA's testing steps start with a short-term test; a result of 4 pCi/L or higher calls for a follow-up test.	U.S. Environmental Protection Agency
Over 8 pCi/L	More than twice the action level.	If the first short-term result is more than twice the 4 pCi/L action level, EPA says to take a second short-term test right away.	U.S. Environmental Protection Agency

EPA on radon levels

Fix at 4 pCi/L: EPA recommends fixing a home when the radon level is 4 pCi/L or more, which EPA writes as 150 Bq/m3.U.S. Environmental Protection Agency, read October 15, 2026
Consider fixing 2 to 4: EPA also recommends that people consider fixing their home when the level is between 2 and 4 pCi/L.U.S. Environmental Protection Agency, read October 15, 2026
No known safe level: EPA states there is no known safe level of radon exposure, which is why it suggests considering a fix below 4 pCi/L.U.S. Environmental Protection Agency, read October 15, 2026
1 pCi/L equals 37 Bq/m3: Results in becquerels per cubic meter convert at 37 Bq/m3 for each 1 pCi/L.U.S. Environmental Protection Agency, read October 15, 2026
US average indoor level: The average indoor radon level in US homes is about 1.3 pCi/L, from a national survey completed in 1991.U.S. Environmental Protection Agency, read October 15, 2026
US average outdoor level: Outdoor air averages about 0.4 pCi/L of radon, according to EPA.U.S. Environmental Protection Agency, read October 15, 2026
Results near 4 are uncertain: EPA explains that when two short-term tests average just over 4 pCi/L, the year-round average could fall either side of 4.U.S. Environmental Protection Agency, read October 15, 2026

When one test is not enough

Step 1: short-term test: EPA's testing steps start with a short-term test; a result of 4 pCi/L or higher calls for a follow-up test.U.S. Environmental Protection Agency, read October 15, 2026
Over 8 pCi/L: retest now: If the first short-term result is more than twice the 4 pCi/L action level, EPA says to take a second short-term test right away.U.S. Environmental Protection Agency, read October 15, 2026
Average two short-term tests: When the follow-up is a second short-term test, EPA says to consider fixing if the two results average 4 pCi/L or higher.U.S. Environmental Protection Agency, read October 15, 2026
Long-term 4 or more: fix: A long-term test result of 4 pCi/L or higher means EPA recommends fixing the home.U.S. Environmental Protection Agency, read October 15, 2026
Results near 4 are uncertain: EPA explains that when two short-term tests average just over 4 pCi/L, the year-round average could fall either side of 4.U.S. Environmental Protection Agency, read October 15, 2026

Short-term and long-term tests

Short-term: 2 to 90 days: Short-term radon tests stay in the home for two to 90 days, depending on the device.U.S. Environmental Protection Agency, read October 15, 2026
Long-term: over 90 days: Long-term tests stay in the home for more than 90 days and usually use alpha track or electret ion chamber detectors.U.S. Environmental Protection Agency, read October 15, 2026
Passive short-term devices: EPA names alpha track detectors, charcoal canisters, charcoal liquid scintillation detectors and electret ion chambers as passive short-term devices.U.S. Environmental Protection Agency, read October 15, 2026
Close up 12 hours before: For a short-term test under four days, windows and outside doors should be closed at least 12 hours before it starts.U.S. Environmental Protection Agency, read October 15, 2026
Closed-house conditions defined: Closed-house conditions mean windows closed, doors closed except for normal entry and exit, and no fans bringing in outside air.U.S. Environmental Protection Agency, read October 15, 2026
Lowest lived-in level: The test kit goes in the lowest lived-in level: the basement if it is used often, otherwise the first floor.U.S. Environmental Protection Agency, read October 15, 2026

Testing again

Below 4: retest sometime: Even with a result under 4 pCi/L, EPA suggests testing again at some point in the future.U.S. Environmental Protection Agency, read October 15, 2026
Retest a newly used level: If you start living on a lower level, such as a basement, EPA says to retest on that level.U.S. Environmental Protection Agency, read October 15, 2026

Set dates for the next test on the retest calendar.

The action level in Illinois, Pennsylvania and Colorado

All three state programs use EPA's 4 pCi/L line.

Action level 4.0 pCi/L: IEMA-OHS and US EPA recommend reducing radon when a home measures 4.0 pCi/L or more.Illinois Emergency Management Agency and Office of Homeland Security (IEMA-OHS), read October 15, 2026
When to fix: DEP advises a second test above 4 pCi/L, and corrective action if the result is still 4 pCi/L or higher.Pennsylvania Department of Environmental Protection, read October 15, 2026
Action level: CDPHE advises testing and mitigating when radon is above 4 pCi/L, the EPA action level, and testing again even when a mitigation system is installed.Colorado Department of Public Health and Environment, read October 15, 2026