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How do you read a radon test result?

By Radon411 Editorial TeamUpdated How we research

Short answer

Read a radon result in picocuries per liter (pCi/L) against EPA's marks: 4 pCi/L is the action level for fixing a home, and 2 to 4 pCi/L is the range to consider a fix. First check the test was valid, and confirm a high short-term result with a followup test.

Next step: pick the right test for your home. Which test to use

Start with the report. It should show where the test was placed, ideally the lowest lived-in level, and its start and stop dates and times; a runs at least 48 hours and a more than 90 days. Improper testing may yield inaccurate results and require another test.

Then the number. The average indoor level is about 1.3 and outdoor air about 0.4. Even levels below 4 pCi/L pose some risk, and radon can be reduced in most homes to 2 pCi/L or below.

A first short-term result that is high needs a followup: a long-term test for the year-round average, or a second short-term test if you need results quickly. The closer an average sits to 4 pCi/L, the less certain the year-round picture.

What to do next: enter your number in the interpreter for a plain reading of what it means and what EPA recommends at that level.

The unit on your report

In the United States, radon results are reported in of air, written pCi/L. , Bq/m3, are also used; that unit counts the number of atomic transformations per second in a cubic meter of air.

Reference points for reading a result
ReferencepCi/LBq/m3
Average outdoor air0.414.8
Average indoor air1.348.1
EPA's action level4148

To convert, 1 pCi/L is 37 Bq/m3, so 4 pCi/L is 148 Bq/m3. See radon levels explained.

Check the test before the number

A number is only as good as the test behind it. Before reading the result, check that the test ran the way it should; improper testing may yield inaccurate results and require another test.

What a valid radon test report should show
ItemWhat to look for
LocationThe lowest lived-in level of the home
Start and stopThe start and stop dates and times were recorded
LengthAt least 48 hours; a long-term test more than 90 days
InstructionsThe kit's testing instructions were followed
LabThe kit was resealed and returned to the lab promptly

If a qualified tester ran the test, or a continuous monitor recorded it, the tester can explain the report, including any unusual swings during the test.

Reading the number

Read the result against EPA's two marks. EPA recommends fixing a home when the radon level is 4 pCi/L or higher. EPA recommends considering a fix when the level is between 2 and 4 pCi/L. Even levels below 4 pCi/L pose some risk, and radon levels can be reduced in most homes to 2 pCi/L or below.

Scale of radon levels from 0 to 10 pCi/L marking EPA's 2 pCi/L level, where EPA says to consider fixing, and its 4 pCi/L action level, where EPA says to fix the home, with each mark also in Bq/m³.
Read this figure as text
  • Below 2 pCi/L (below 74 Bq/m³)Below both of EPA's guidance levels.
  • 2 to 4 pCi/L (74 Bq/m³ to 148 Bq/m³)EPA recommends considering a fix when the level is between 2 and 4 pCi/L.
  • At or above 4 pCi/L (148 Bq/m³ and up)EPA recommends fixing a home when the radon level is 4 pCi/L or higher.
Where a result sits against EPA's marks at 2 and 4 pCi/L, in both units.

For a closer reading of a specific number, see what 2, 4, 5 and 10 pCi/L mean.

A first short-term result: confirm it

Because radon varies from day to day and season to season, a single short-term result is a starting point. If it is high, take a followup test to be sure: a for a better picture of the year-round average, or a second if you need results quickly.

Flowchart of EPA's radon testing steps: take a short-term test; at or above 4 pCi/L follow up with a long-term or a second short-term test; then fix the home or consider fixing based on the result or the average of the two tests.
Read this figure as text

  1. 1Step 1: Take a short-term test.

    • Below 4 pCi/LEven if your test result is below 4 pCi/L, you may want to test again sometime in the future.
    • At or above 4 pCi/LIf your result is at or above 4 pCi/L, take a followup test to be sure.

  2. 2Step 2: Follow up with either a long-term test or a second short-term test.

    • Long-term testFor a better understanding of your year-round average radon level, take a long-term test.
    • Second short-term testIf you need results quickly, take a second short-term test. If your first short-term test result is more than twice EPA's 4 pCi/L action level, you should take a second short-term test immediately.

  3. 3Step 3: Decide whether to fix your home.

    • After a long-term testFix your home if your long-term test result is 4 pCi/L or more.
    • After a second short-term testConsider fixing your home if the average of your first and second test is at or above 4 pCi/L.
From a first short-term test to a follow-up, then to a decision to fix or consider fixing.
Choosing the follow-up
First resultFollow-up
High, and you have timeA long-term test, for the year-round average
High, and you need results quicklyA second short-term test
More than twice EPA's 4 pCi/L action levelA second short-term test immediately

Reading a monitor's report or a seller's result

Not every result comes from a mailed kit. Many continuous monitors provide a report that can reveal unusual or abnormal swings in the radon level during the test period, and a qualified tester can explain that report to you. In a home sale, if the seller or the tester cannot confirm that every item on the testing checklist was completed, take another test.

What to check on each kind of result
ResultCheck
Lab report from a kitThe location, the start and stop dates and times, and the result in pCi/L
Continuous monitor reportThe average for the test period, and any unusual swings
A seller's earlier resultThat every checklist item was completed; if not, test again

Two results that disagree

With two short-term tests, the higher the results, the more certain you can be that you should fix the home. The closer their average is to 4 pCi/L, the less certain you can be whether the year-round average is above or below that level, so a long-term test helps when the numbers sit near the line.

Questions about reading a radon test

What does pCi/L mean on a radon test?

Picocuries per liter of air, the unit used for radon in the United States.

What is a good radon test result?

The lower the better. The average indoor level is about 1.3 pCi/L, and radon can be reduced in most homes to 2 pCi/L or below.

How do I convert Bq/m3 to pCi/L?

Divide by 37. EPA's 4 pCi/L action level is 148 Bq/m3.

What if my two tests are different?

Use their average. The closer it is to 4 pCi/L, the less certain the year-round picture, so a long-term test can settle it.

How long until I get my results?

You should receive results from a lab within a few weeks.

Should I retest after a low result?

You may want to test again sometime in the future, and retest if you start using a lower floor or renovate.

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