What Should Radon Levels Be? A Plain Guide
After a radon test produces a number, the obvious question follows: is that good or bad? Homeowners want a clear benchmark to judge their result against, and understanding what should radon levels be turns an abstract figure into an actionable decision. This guide summarizes EPA and CDC guidance current as of 2026 and is informational only; it does not diagnose any condition, and a certified professional should make testing and mitigation decisions for your home. Below, we explain the EPA action level of 4 pCi/L, what the numbers mean in context, why no level is entirely risk-free, and how Front Range homeowners should interpret their results.
What Should Radon Levels Be in a Home?
The clearest benchmark comes from the EPA, which recommends taking action to reduce radon when indoor levels reach or exceed 4 pCi/L (picocuries per liter of air). That figure is the action level, and it is the number to anchor to when interpreting any radon test result.
It is important to understand what the action level is and is not. It is not a sharp line between safe and dangerous, like a poison threshold. It is the level at which the EPA recommends mitigation because the long-term lung-cancer risk becomes significant enough to warrant action and because mitigation can reliably reduce levels at and above it. Below 4 pCi/L, mitigation is not formally recommended, but the risk is not zero.
So the short answer to what radon levels should be is: as low as reasonably achievable, with 4 pCi/L as the threshold that triggers a clear recommendation to act. A result at or above that number means you should pursue mitigation; a result below it means lower risk, though not the complete absence of risk.
Understanding the Numbers
Radon is measured in picocuries per liter of air in the United States, abbreviated pCi/L. Putting common readings in context helps make sense of a test result.
- At or above 4 pCi/L: The EPA recommends mitigation. The higher the number, the more urgent the action.
- Between 2 and 4 pCi/L: Below the action level, but the EPA notes that homeowners may consider reducing levels in this range, since risk persists.
- Below 2 pCi/L: Lower risk, and difficult to reduce much further, since some radon exists in outdoor air.
For perspective, outdoor air typically contains a low background level of radon, often well under 1 pCi/L. Indoor air can concentrate radon far above that because homes draw soil gas inside through the stack effect. No home can realistically reach zero, so the goal is reducing elevated indoor levels toward the low background range, not eliminating radon entirely.
The way radon is measured also affects interpretation. Short-term tests give a quick snapshot that can be influenced by weather and how the home was operated, while long-term tests average exposure over months for a truer picture. Our guide on how radon is measured explains why the testing method matters when judging a result.
Why No Radon Level Is Truly Risk-Free
A common misconception is that staying below 4 pCi/L means the home is safe and radon can be ignored. The reality is more nuanced. Radon is a known cause of lung cancer, and the risk it poses is generally understood to follow a linear relationship: lower levels carry lower risk, but the risk does not drop abruptly to zero just below the action level.
The EPA chose 4 pCi/L as a practical action level, balancing health risk against what mitigation can reasonably achieve, not as a guarantee of safety below it. Some risk remains at levels between 2 and 4 pCi/L, which is why the EPA suggests homeowners may consider reducing radon in that range as well, particularly if it can be done easily.
This framing matters because it shifts the goal from “passing” a threshold to minimizing exposure. The health concern with radon is entirely long-term: prolonged exposure raises lifetime lung-cancer risk, and the danger is greatest for smokers, in whom radon and tobacco risks multiply. The principle of keeping levels as low as reasonably achievable reflects the fact that every reduction in exposure reduces risk. The connection between radon and disease is explored further in our overview of radon and lung cancer.
What to Do at Each Level
A test result points to a clear course of action depending on where it falls relative to the benchmark.
At or Above 4 pCi/L
Pursue mitigation. For real-estate or initial screening done with a short-term test, a confirmatory test is sometimes advisable before committing to a system, since short-term results fluctuate. Once confirmed, a qualified mitigation contractor can install a system, most commonly active sub-slab depressurization, that reliably brings levels down.
Between 2 and 4 pCi/L
No formal mitigation is required, but consider whether reducing the level makes sense for your household, especially if anyone smokes or spends many hours in a lower-level living space. At minimum, retest periodically to confirm the level remains stable.
Below 2 pCi/L
The result is reassuring and near the practical floor. Continue periodic retesting, particularly after renovations or foundation work that could change airflow. Maintain awareness without alarm.
Regardless of the result, retesting matters because radon levels change over time with weather, season, and modifications to the home. A single test is a snapshot, not a permanent verdict.
Why Testing Method Affects the Number
A radon result is only as meaningful as the test that produced it, so understanding how the measurement was taken is part of interpreting whether a level is acceptable. The same home can yield different readings depending on the test type, duration, and conditions during the measurement.
Short-term tests, lasting from a few days to about a week, are quick and well suited to real-estate transactions. Their drawback is sensitivity to short-term conditions: weather, barometric pressure, and how the home was operated during the test all influence the result. A short-term test conducted during an unusual weather pattern, or in a home where windows were opened, may not reflect the typical level. For this reason, a single short-term result is best treated as a screening snapshot rather than a definitive verdict.
Long-term tests run for more than 90 days and average exposure across changing conditions and seasons, producing a more accurate picture of what occupants actually breathe over time. They are ideal for homeowners assessing a property they already own, though their timeline rarely fits a closing window. When a short-term test returns a borderline or elevated result, a follow-up test, sometimes a second short-term test under controlled closed-house conditions, helps confirm the level before committing to mitigation. Comparing the two test types side by side makes it easier to judge a borderline result in context.
Common Misconceptions About Radon Levels
Several persistent myths lead homeowners to misjudge their radon results. Clearing them up helps put any number in proper perspective.
- “My neighbor tested low, so my home is fine.” Radon levels vary significantly between adjacent homes because of differences in foundation, soil, and the stack effect. Only testing your own home reveals your level.
- “New homes do not have radon.” Radon depends on geology and entry pathways, not construction date. Newer homes test high as readily as older ones.
- “Below 4 pCi/L means zero risk.” The action level is a practical threshold, not a guarantee of safety. Risk declines with the level but does not vanish just below 4 pCi/L.
- “One test settles it forever.” Levels change with weather, season, and home modifications, so periodic retesting matters.
- “Radon is only a basement problem.” While levels are usually highest on the lowest level, radon can reach upper floors, and exposure depends on where occupants spend time.
Each misconception encourages complacency, and complacency is precisely what radon exploits. Because the gas gives no warning, accurate understanding of what a level means is the homeowner’s best protection.
The Front Range Context
Colorado homeowners interpret these numbers against a backdrop of elevated regional radon. The Front Range’s uranium-bearing geology and the prevalence of basements mean many local homes test at or above 4 pCi/L, sometimes well above. EPA radon-zone mapping places much of the region in higher-risk categories.
This makes testing especially important here, and it also means a high result is common rather than alarming. Front Range homeowners frequently find levels that warrant mitigation, and the region has many qualified contractors as a result. A high reading is not a sign that something is wrong with the home; it reflects the geology beneath it, and it is readily addressed.
Because levels can vary even between neighboring homes, Colorado homeowners should test their own house rather than assume their level matches a neighbor’s. Newer homes are not exempt; radon depends on geology and entry pathways, not construction date. The full process, from first test through verified mitigation, is laid out in our radon testing guide for Front Range homeowners.
Turning a Number Into a Decision
The value of knowing what radon levels should be is that it converts a test result into a clear next step. Measure your home, compare the result to the 4 pCi/L action level, and act accordingly: mitigate at or above it, consider reducing in the 2 to 4 range, and retest periodically at any level.
Keep the broader truth in view. Radon causes no symptoms and offers no warning, so the number from a test is the only signal you will ever get. Treating that number seriously, rather than waiting to feel an effect that never comes, is the entire strategy for managing radon safely.
The reassuring side is that radon is both measurable and fixable. Whatever your result, you have a clear benchmark to judge it against and a proven path to lower an elevated level. Anchoring to 4 pCi/L while aiming as low as reasonably achievable gives Front Range homeowners a sound, evidence-based way to protect the long-term health of their households.
How Other Standards Compare to the EPA Level
Homeowners who research radon sometimes encounter different reference numbers and wonder which to trust. Understanding how various standards relate to the EPA action level helps put your result in context without confusion.
The EPA action level of 4 pCi/L is the primary benchmark used in the United States, and it is the figure most relevant to American homeowners and real-estate transactions. The EPA additionally notes that homeowners may consider reducing levels between 2 and 4 pCi/L, reflecting that risk persists below the action level. This two-tier framing, a firm recommendation at 4 and a consideration at 2, captures the agency’s risk-based approach.
Internationally, some health bodies express radon guidance using different units and somewhat lower reference levels, reflecting a similar underlying goal of minimizing exposure. Those who measure radon in becquerels per cubic meter rather than picocuries per liter will see different numbers for the same concentration, since the units differ. For practical purposes in the United States, the EPA’s 4 pCi/L remains the standard to apply, with the understanding that lower is always better.
The consistent message across all these standards is the same one that should guide a homeowner: radon risk rises with exposure, no level is entirely risk-free, and reducing elevated levels protects health. Rather than getting lost in competing figures, anchor to the EPA action level, aim as low as reasonably achievable, and let a test of your own home drive the decision. That approach aligns with the science and gives Front Range households a clear, defensible basis for action. In the end, the question of what radon levels should be has a practical answer that any homeowner can apply. Test your own home, read the result against the 4 pCi/L action level, mitigate if you are at or above it, consider reducing levels in the 2 to 4 range, and retest periodically. The number on a radon report is the only signal radon will ever give you, so treating it seriously is the entire strategy for keeping a home safe.
References
- EPA Action Level for Radon — U.S. Environmental Protection Agency
- About Radon — Centers for Disease Control and Prevention
- Colorado Radon Program — Colorado Department of Public Health and Environment
Front Range homeowners trying to make sense of a radon result can reach a vetted local professional through our contact page to discuss what the number means and what to do next.