How to Read Radon Test Results

On this page (7 sections)

1. What do the numbers on a radon test report mean?
2. Why do the sampling dates and test duration matter?
3. What does an average radon result tell you?
4. What should you do with a result at or above 4 pCi/L?
5. Should you repeat a test with a low or unclear result?
6. Which parts of a radon report should you keep?
7. How to read radon test results and choose a next step

To read radon test results, check the concentration in pCi/L, the sampling dates, and the test duration, then compare the reported average with the EPA action level of 4 pCi/L. A short-term result is a snapshot; a follow-up test can help determine whether it reflects the home's longer-term level.

A radon report can look technical, but a few details make it easier to understand. Confirm that the sample was collected as directed before deciding what to do.

What do the numbers on a radon test report mean?

The main number is the measured radon concentration, usually reported in picocuries per liter (pCi/L). Higher numbers indicate a higher concentration in the tested air during the sampling period.

Check the unit before comparing results. Some reports may use a different unit, so ask the lab or testing provider how to compare it with U.S. guidance if pCi/L is not shown.

The number describes the test conditions and period. It does not tell you that every room has the same level or that a later test will match exactly.

For context on common readings, use this radon levels chart. For details on setting up a test in the first place, see How to Check Radon Levels: What That Means.

Why do the sampling dates and test duration matter?

The dates and duration show when the sample was collected and how long the detector was exposed. Compare those details with the instructions that came with your test.

Look for the start and end dates, or the total exposure time. Some reports also show when the lab received or analyzed the sample; those dates are different from the days the detector sat in your home.

If dates are missing or seem wrong, contact the lab or testing provider before treating the result as a reliable measure of the test period. Keep the report and any notes about placement or interruptions.

What can change a radon test result?

Room placement, closed-house conditions, weather, and the test method can affect a reading. Follow the kit's instructions for where to place the detector and how to manage doors, windows, and ventilation during testing.

A test that was moved, covered, exposed to unusual conditions, or left out longer or shorter than directed may not represent the intended sample. Rain can also affect a reading; see whether radon levels rise when it rains.

Read what can affect a radon test before deciding whether to repeat it.

What does an average radon result tell you?

An average summarizes the measurements included in that report, but the report should identify what was averaged and over what period. A single short-term test is not the same as an average from multiple tests or a long-term test.

Read any notes beside the result. They may explain whether the number reflects one detector, several measurements, or a longer sampling window.

Don't average separate results yourself unless the testing provider or a qualified professional tells you how. For two results, relative percent difference is one way to describe how far apart they are.

Different test lengths and conditions can make a simple calculation misleading.

A long-term radon test can give a better picture of average exposure over time because it runs for more than 90 days. Follow the relevant test instructions and guidance for your home.

What should you do with a result at or above 4 pCi/L?

If a test result is at or above 4 pCi/L, follow EPA guidance and arrange a follow-up test or mitigation advice. The EPA recommends fixing homes at or above this level, while noting that no radon level is known to be risk-free.

The next test depends on the result and the type of first test. EPA guidance generally calls for a second short-term test when the first result is 4 to 10 pCi/L, and either a second short-term test or a long-term test when it is above 10 pCi/L.

If the average of two tests is 4 pCi/L or higher, EPA recommends fixing the home. Consider a qualified radon professional to explain testing and mitigation options.

A low result is useful, but it is not a guarantee that levels will always stay low. Retest after major renovations or changes to the home's foundation, and follow local guidance for real estate transactions.

Should you repeat a test with a low or unclear result?

Repeat the test if the report is unclear, the detector may not have been used as directed, or you want to understand the home's level over a longer period. A low short-term reading can vary with conditions and does not rule out future changes.

If you're unsure how much confidence to place in one result, read How Accurate Are Radon Tests? What Experts Say.

You can also review how to test for radon at home before starting another test.

A lab-based kit may suit a reader who wants a mail-in sample and a written result. The First Alert kit includes test materials and lab fees, with New Jersey state fees excluded; results are emailed within 72 hours of lab receipt.

The PRO-LAB kit is a short-term option with a 48-hour sample period and lab analysis included. Its results are delivered by email or text notifications.

The Leaping Lynx kit uses a 48-hour short-term sample and includes lab analysis; postage is required to return the detector. Its instructions call for placement on the lowest livable level.

Choose a kit based on its test period, return steps, and instructions for your home. Use only the results from the lab or testing provider for that specific sample.

Which parts of a radon report should you keep?

Keep the full report with its dates, units, test duration, and any lab notes. These details help a qualified professional understand how the result was obtained.

Record the room and floor where the detector was placed, along with any issue that may have affected the sample. Save the test instructions too, so you can check whether the procedure was followed.

For a result near or above 4 pCi/L, use the report to plan the follow-up with a radon professional. If the reading is confusing, ask the lab what the reported average covers before making a decision.

How to read radon test results and choose a next step

When you read radon test results, start with the unit, dates, duration, and reported concentration. Then compare the value with EPA guidance and consider whether the sample conditions support a follow-up test.

For a result at or above 4 pCi/L, follow up and ask a qualified radon professional about fixing the home. For a low or uncertain result, repeat testing if conditions or your goal call for a clearer long-term picture.

Frequently asked questions

What units do radon test results use?

Most U.S. home radon results are reported in picocuries per liter, written pCi/L. Compare results in the same unit, and don't confuse the concentration with the number of days the test ran.

If a report uses another unit, ask the lab or testing provider how to interpret it before comparing values.

Is a radon result of 4 pCi/L safe?

The EPA recommends fixing a home at or above 4 pCi/L, but no radon level is known to be risk-free. A result below 4 pCi/L can still be a reason to consider reducing exposure, especially if you want a clearer picture from a longer test.

Discuss next steps with a qualified radon professional.

Should I repeat a radon test if the result is high?

A high short-term result generally calls for a follow-up test, following EPA guidance and the test provider's instructions. Depending on the first result, the next step may be another short-term test or a long-term test.

If the average of two tests is 4 pCi/L or higher, the EPA recommends fixing the home.

What does a radon test report include?

A report commonly gives the measured radon concentration, unit, sample or test dates, and testing duration. It may also include the lab's analysis date and instructions for next steps.

Check that the dates match your test and that the detector was exposed for the full period required by its instructions.