How to Read Your Radon Test Results

Updated May 2026 · A plain-English guide to test result numbers

You ordered a radon test kit, mailed in the sample, and got a number back — maybe 2.1, maybe 4.5, maybe 12. Now what? This guide explains what radon test results actually mean, how to interpret the number you got, and what your reasonable next steps are.

The short version: the EPA action level is 4.0 pCi/L. If your average reading is at or above that number, the EPA recommends taking action. If it's below, there are still some considerations — read on.

What pCi/L actually means

Radon test results in the United States are reported in picocuries per liter, abbreviated pCi/L. It's a measure of how much radioactive radon gas is in the air. Higher number = more radon = higher long-term lung cancer risk.

Some context for the numbers:

0.4 pCi/L — average outdoor radon concentration in the U.S.
1.3 pCi/L — average indoor radon concentration nationally
4.0 pCi/L — the EPA action level (mitigation recommended at or above this)
5.5 pCi/L — Iowa's average residential radon level (highest in the U.S.)
20+ pCi/L — high reading; not unusual in central Iowa basements
100+ pCi/L — uncommon but does occur; mitigation is urgent

For perspective: living in a home at 4.0 pCi/L for a lifetime carries roughly the same lung-cancer risk as smoking half a pack of cigarettes a day. At 20 pCi/L, the risk is comparable to smoking two packs a day. The EPA estimates radon causes about 21,000 lung cancer deaths in the U.S. each year — the leading cause among non-smokers.

Step 1: Find your average reading

Pull up your test result and find the number labeled "average," "result," or "pCi/L." This is the value you compare to 4.0.

A few notes depending on test type:

Long-term test (90+ days): the most accurate result. The number reflects an average over multiple seasons and is the most reliable indicator of your home's typical radon exposure.
Short-term test (2–7 days): faster but less accurate. Short-term tests are sensitive to weather, season, and whether windows were closed during the test. Treat the result as a snapshot, not a long-term average.
Continuous radon monitor (professional test): usually most accurate of the short-term options. Often used during real-estate inspections.

Step 2: Compare to the action level

Once you have your number, here's what it generally means:

Below 2.0 pCi/L — Low risk. The EPA still recommends retesting every two years to catch any changes (HVAC modifications, slab cracks, etc. can change radon levels over time).

2.0 to 3.9 pCi/L — Below the action level, but elevated relative to outdoor air. The EPA recommends "considering" mitigation in this range — many Iowa homeowners choose to mitigate proactively because of the lung cancer risk associated with long-term exposure even at sub-action levels. At minimum, retest in a year, ideally with a long-term test.

4.0 pCi/L or higher — Above the EPA action level. Mitigation is recommended. The next step is to confirm the result with a second test (especially if the first was a short-term test) or schedule an estimate from a licensed mitigator.

Step 3: Decide whether to confirm or proceed

For results just above the action level (4.0–6.0 pCi/L) from a short-term test, the EPA recommends a follow-up test before mitigating. Options:

A second short-term test, run for 2–7 days
A long-term test, run for 90+ days
A simultaneous side-by-side test (two test devices placed in the same room)

For results well above the action level (above ~8 pCi/L), the EPA generally recommends moving directly to mitigation rather than waiting for a long-term follow-up — the higher the number, the less ambiguous the recommendation.

For results from a long-term test, no follow-up is typically needed before mitigation — long-term tests are accurate enough on their own.

Step 4: If you decide to mitigate

The standard next step is to get an estimate from a licensed Iowa mitigator. The estimate is free, takes about thirty minutes on-site, and gives you a written quote. From there:

Compare the quote to the published industry ranges (see our Iowa pricing guide).
If you have an existing passive radon system (common in newer Iowa homes), conversion to active is generally less expensive than a full new install.
Schedule the install (most are completed in a single day).
Run a post-mitigation test 24+ hours after the system starts running to confirm the level dropped below 4.0 pCi/L.

Common situations and what they mean

"My short-term test was 6.2 pCi/L but my long-term test was 3.8 pCi/L. Which is right?"

The long-term test is generally more accurate because it averages over seasonal variation. Radon levels are typically higher in winter (when homes are sealed up) and lower in summer (when windows are open). A short-term winter test can read significantly higher than the year-round average. In this scenario, your true average is likely closer to 3.8, but the winter peaks above 6 are real and worth taking seriously. Many homeowners in this situation choose to mitigate anyway.

"My basement reads high but my main floor reads low. Should I still mitigate?"

Yes. Mitigation guidance is based on the lowest livable level of the home — usually the basement, even if you don't currently use it as living space. A high basement reading means radon is entering the home; if the basement is ever finished or used regularly, exposure increases. Mitigation also protects the home's resale value, since a future buyer's inspection will test the basement.

"I just bought a home that has a mitigation system. Should I test it?"

Yes. Mitigation systems can fail (the fan can wear out, the system can be unplugged). The seller's old post-mitigation test is typically several years old at the time of sale. Run a fresh short-term test to confirm the existing system is still keeping levels below the action level. Most hardware-store kits work fine for this confirmation.

"I'm pregnant / have young children. Does the action level still apply?"

Yes — the 4.0 pCi/L action level is the EPA's general guidance for residential mitigation. Long-term radon exposure increases lung cancer risk for everyone, but the EPA does not have separate action levels for specific populations. Some homeowners with young children or other health-sensitive household members choose to mitigate at lower readings (in the 2.0–4.0 range) for additional precaution.

"My test result came in at 200 pCi/L. Is that a typo?"

Probably not. Iowa has documented homes with readings well above 100 pCi/L. If your result is genuinely above 50 pCi/L, the EPA recommends mitigating quickly rather than waiting for a follow-up test. Call a mitigator and explain the reading — they can prioritize the work.

"My test result is 'less than 0.5 pCi/L'. Did the test fail?"

Probably not — that's just below the lower detection limit of the test device. Such a low reading is genuinely possible, especially in homes with effective air sealing or a working mitigation system already in place. No action needed beyond the standard 2-year retest.

Tools and resources

Inexpensive long-term test kits ($20–$30) at hardware stores or by mail order
The EPA's Citizen's Guide to Radon
The Iowa HHS radon resources page
The state's published list of credentialed Iowa radon mitigation specialists

Next step

If your result is above 4.0 pCi/L and you'd rather skip the second test and move toward mitigation, the on-site estimate is free and takes about thirty minutes. We can also walk through your test result on the phone if you want a quick sanity check before scheduling.

📞 Call (515) 495-5632 Or request a callback

This article summarizes EPA guidance and standard Iowa residential radon-testing practice. It is not medical advice. Individual health considerations may warrant different approaches — consult your physician for advice specific to your situation.