Radon Levels Explained: What Your pCi/L Reading Means
Radon is measured in picocuries per litre of air, written pCi/L. The EPA recommends fixing a home at 4.0 pCi/L or higher, and recommends considering action between 2.0 and 4.0. For context, the average indoor level in the United States is about 1.3 pCi/L and the average outdoors is roughly 0.4 pCi/L.
One thing to be clear about before any number: no level of radon is proven safe. 4.0 pCi/L is an action threshold, not a safety line. A lower reading means lower exposure, not none — so nothing on this page describes a result as safe, and you should be wary of anyone who does.
Check your reading
Enter the number from your radon report. Every band is listed in the table below as well.
Radon levels chart
Every band, what the EPA says about it, and what it means for a home in Colorado.
| Reading (pCi/L) | Bq/m³ | What the EPA says | What to do |
|---|---|---|---|
| Below 2.0 pCi/L | 0–73 | Below the level at which the EPA suggests considering action. | No mitigation is indicated. Retest every two years, and again after any work that changes your foundation or how tightly the house is sealed. |
| 2.0 – 3.9 pCi/L | 74–147 | In the range where the EPA suggests you consider taking action. | Consider a long-term test to establish your year-round average before deciding, and consider mitigation if the lower level is occupied living space. |
| 4.0 – 7.9 pCi/L | 148–295 | At or above the EPA action level. The EPA recommends fixing the home. | Confirm with a follow-up test, then install an active mitigation system. A long-term follow-up test gives the better picture of your year-round average at this level. |
| 8.0 – 19.9 pCi/L | 296–739 | Well above the EPA action level. | A second short-term test confirms the result faster than a long-term test at this level. Arrange mitigation without waiting for a seasonal average. |
| 20.0 pCi/L and above | 740+ | Substantially above the EPA action level. | Confirm with a second short-term test and arrange mitigation promptly. Reduce time spent in the lowest level of the building until a system is in place and verified. |
pCi/L and Bq/m³
The United States measures radon in picocuries per litre (pCi/L). Most of the rest of the world uses becquerels per cubic metre (Bq/m³). One pCi/L equals 37 Bq/m³, so to convert, multiply pCi/L by 37, or divide Bq/m³ by 37.
That puts the EPA's 4.0 pCi/L action level at 148 Bq/m³, and the World Health Organization's reference level of 100 Bq/m³ at about 2.7 pCi/L — a lower threshold than the EPA's.
What a single reading does and does not tell you
A short-term test is a snapshot. Radon concentrations move with weather, season and how a building is being used, and a heated house pulls harder on the soil gas beneath it when it is cold outside — so the same house often reads higher in January than in July.
That is why an elevated short-term result is normally confirmed. A long-term test (more than 90 days) gives the better picture of your year-round average and is the sensible follow-up when the first reading is a little over the action level. A second short-term test is quicker and is the more practical choice when the first reading was well above it, or when a property sale is on a deadline.
It is also why a neighbour's result tells you nothing about your own. Radon depends on your specific foundation, your soil contact and how your building moves air. Houses on the same street routinely differ by several pCi/L.
In this county the base rate is high enough that testing is worth doing regardless. El Paso County is EPA Radon Zone 1, county public health reports over 40% of homes tested between 2005 and 2023 came back elevated, and CDPHE puts the statewide figure at roughly 1 in 2 homes. A professional radon test is a flat $150 with results in about 48 hours.
If your number is at or above the action level, an active mitigation system is the fix, and the EPA states these can reduce levels by up to 99%. What happens during a mitigation install walks through it. If you are buying or selling, Colorado's radon disclosure rules apply.
Common questions about radon readings
Direct answers for the numbers people search for most.