What does my radon result mean?
A radon result is not self-explanatory, because the same number means different things depending on where it was measured, when, and how the space is used. This tool applies the published guidance bands to your reading, then adjusts the interpretation for the conditions you describe.
It returns reasoning rather than a verdict. Everything it applies is listed under “the logic, in full” below, so you can check the reasoning rather than trust the output.
Work it through
Everything below runs in your browser. Nothing you enter is sent to us or to anyone else — this page has no server to send it to.
The average reported by the device or laboratory.
Where the device sat.
Weather during the measurement changes what the number represents.
Short-term is a snapshot; long-term is an annual-scale average.
Windows and exterior doors closed for 12 hours before and throughout, whole-house fans off.
Whether the measured level is living space rather than storage.
What this indicates
Reading your inputs…
What is established, and what is not
Two groups, weighted the same. An item in the second group is an open question rather than a problem — most of them are the ordinary condition of a home test, and none of them is a mark against your house.
What nobody has established
Not failures, and not things you did wrong. Each one is answerable — by a laboratory, by a professional on site, or by a longer measurement — and none of them has been answered yet.
Device calibration
Not established
A device reports what it reports. Whether it was calibrated, and when, is a property of the device and its programme rather than of the reading.
Chain of custody
Not established
Where the device was between the end of the test and the analysis affects what the result describes, and only the handling record shows it.
Placement compliance
Not established
Whether placement actually met protocol depends on distances and surfaces nobody has measured from here, however carefully it was described.
Interference during the test
Not established
A door propped open for an afternoon, or a device moved and moved back, would not appear in any record a homeowner holds.
Seasonal variation in this house
Not established
The same house commonly reads differently in different seasons, and a single test covers one period rather than a year.
Readings on other floors
Not established
A measurement describes the level it was taken on. What the rest of the house reads is a separate question with a separate answer.
Categories a next step could fall into
Unordered, and none of them is a recommendation. Which one applies depends on things this page does not know.
Why this says what it says
The full working, shown rather than summarised. Nothing below is hidden behind a toggle, because reasoning that takes a click to reach has not really been shown.
What you told us, and what each answer did
| Your answer | Value | What it influences |
|---|---|---|
| Your result | 4.2 pCi/L | The average reported by the device or laboratory. |
| Floor measured | Lowest lived-in level | Where the device sat. |
| Season | Heating season | Weather during the measurement changes what the number represents. |
| Test length | Short-term (2–7 days) | Short-term is a snapshot; long-term is an annual-scale average. |
| Closed-building conditions held | Yes | Windows and exterior doors closed for 12 hours before and throughout, whole-house fans off. |
| Space is used daily | Yes | Whether the measured level is living space rather than storage. |
What we took on trust
- The figures you enter (your result) are taken exactly as typed. We have no way to check them against a device or a laboratory record.
- Your answers about floor measured, season, test length are taken as described. Where a description is approximate the output is approximate in the same way.
- The yes/no conditions (closed-building conditions held, space is used daily) are accepted exactly as you set them. Nobody has confirmed any of them, and the output assumes each is as stated.
What is still unknown
- What your house would read on a different day, in a different season, or under different weather. One measurement is one sample.
- How your result compares to other houses on your street, because we hold no measurement data by area and area averages do not describe individual addresses anyway.
- What your specific health risk is at your specific concentration and exposure duration. That is a question for a physician, not a web tool.
Why this stops short of a decision
This runs entirely on what you typed. Nobody has been to your house, nobody has seen the device or the laboratory record, and the choice between courses of action follows from diagnostics performed on the building. What you have here is a reading of what you reported, which is a different thing from a decision and a good basis for making one.
What would change this
- A long-term alpha-track measurement over ninety days or more in your own house would settle what you actually live with across seasons — that is a real answer this tool cannot give you.
- Paired short-term and long-term measurements in the same house would quantify your specific seasonal swing rather than describing the general pattern.
- Correcting any answer above. Change an input and the output changes, which is the honest behaviour of something working from a description.
The logic, in full
These are the rules the tool applies — not a summary of them. The interactive panel above evaluates exactly this list, and a build check fails if the two ever diverge. A decision tool whose reasoning you cannot inspect is a black box, and a black box is not authority.
| When | Then |
|---|---|
| Result is 4.0 pCi/L or above | EPA recommends taking action to reduce the level. This is the action level, not an emergency and not a safety boundary. |
| Result is 2.0 to 3.9 pCi/L | EPA suggests considering action. A household judgement rather than a mandate — weigh who lives there, how the lowest level is used, and how long you plan to stay. |
| Result is below 2.0 pCi/L | No action is recommended. That is guidance about what to do, not a verdict on exposure — lower is still better, and EPA notes some risk remains at any indoor concentration. |
| Closed-building conditions did not hold | The measurement is invalid rather than merely imprecise. Ventilation usually pushes a reading down, so a compromised test that still reads high may understate the true number. Re-run it properly before deciding anything. |
| Measured on an upper floor | The result understates the lowest lived-in level, which is the comparable benchmark. Re-measure on the lowest level you occupy or reasonably could before acting on this number. |
| Short-term test in mild or cooling weather | This is closer to the low end of your range. Heating-season stack effect draws harder on the soil, so a winter measurement is the more conservative planning number. |
| Short-term test within 0.6 of the action level | Close enough to the line that weather and conditions could move it either side. A second short-term test, or a long-term detector, costs a fraction of the decision it informs. |
| Long-term test at any level | This is closer to the exposure you actually live with across seasons, and is the stronger basis for a decision in the 2–4 band. |
| Result at or above 4.0 and space is used daily | Both the concentration and the exposure time point the same way. Get written quotes from credentialed contractors that include a post-mitigation verification test. |
| Result at or above 4.0 in a storage-only basement | Exposure is lower than in a finished room, but a basement is the lower end of the house’s stack effect and what accumulates there moves upward. Decide on the whole-house picture rather than the room’s usage alone. |
What this tool cannot do
- This tool interprets a number you already have. It cannot tell you what a system would cost, whether a contractor is any good, or what your house would read on a different day.
- It applies general guidance. Where a state or a contract specifies a different threshold or procedure, that specification governs.
- Nothing here is medical advice. Questions about health risk to a specific person belong with a physician.
Related
- Should I retest? — Time since the last test, plus what has changed in the house — the two things that decide it.
- Selling or buying? — Your side, your timeline, your result — and what should be in the amendment.
- How testing works — Devices, placement, closed-building conditions, and what invalidates a result.
- False positives — Most disputed results are not false — they are invalid, mismeasured, or comparing two different things.
- Weather effects — Weather genuinely moves indoor radon — but it explains variation around a number, not a number well above the action level.
- Radon Testing Method Comparison Dataset — Which method answers which question — and which decisions each one cannot carry.
- Radon Terminology Dataset — Controlled vocabulary with the misreading each term reliably attracts.
- All tools — every calculator and decision tool.
Confidence and limits of this page
Every decision resource on this platform states its own boundaries. This is not a disclaimer — it is the part of this tool you should read before relying on it.
- What we knowClaims on this page we stand behind, each traceable to an approved source or to observable structure.
- EPA recommends action at 4 pCi/L and recommends considering action between 2 and 4 pCi/L. Both figures come from EPA publications, not from us.
- Short-term measurements vary with season, weather, and whether closed-building conditions were maintained. That variation is well established and is why the tool weighs your conditions alongside your number.
- Measurement convention places the device on the lowest lived-in level because that produces a conservative, comparable figure across houses.
- What we do not knowQuestions you may reasonably have that this page does not answer.
- What your house would read on a different day, in a different season, or under different weather. One measurement is one sample.
- How your result compares to other houses on your street, because we hold no measurement data by area and area averages do not describe individual addresses anyway.
- What your specific health risk is at your specific concentration and exposure duration. That is a question for a physician, not a web tool.
- What research would settle itWhat it would actually take to answer the above — naming it is the difference between honesty and hedging.
- A long-term alpha-track measurement over ninety days or more in your own house would settle what you actually live with across seasons — that is a real answer this tool cannot give you.
- Paired short-term and long-term measurements in the same house would quantify your specific seasonal swing rather than describing the general pattern.
- What we do not claimClaims you might expect to find here and will not, with the reason.
- We do not claim any result is safe. EPA notes some risk remains at any indoor concentration, and no band on this page is described otherwise.
- We do not claim what mitigation would cost you. This platform holds zero quote observations and publishes no price benchmark anywhere.
- We do not claim your result predicts a neighbour's, or that a neighbour's predicts yours.
- What we cannot independently verifyFacts this page relies on that we could not confirm ourselves.
- Whether your device was correctly placed and your conditions genuinely held. The tool takes your word for both, and its output is only as good as those inputs.
- Whether the laboratory or device that produced your number is currently in good standing. Verifying that is a question for your state programme.
What to do with a radon result
What it shows. That the first question is test validity, not the number — where most disputed results actually resolve.
Authored as SVG in this repository, with real text nodes and a long description for screen readers. Reusable under CC BY 4.0 — see the diagram library.
Sources
- U.S. EPA — Radon
- U.S. EPA — A Citizen’s Guide to Radon
- U.S. EPA — Health Risk of Radon
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