What radon level is dangerous?

EPA recommends fixing a home at 4 pCi/L or higher and considering a fix between 2 and 4 pCi/L. EPA also says there is no known safe level of radon exposure.

Should I retest before fixing radon?

If the result came from a single short-term test, yes. Confirm with a second short-term test or a long-term test; EPA guidance is to fix if a long-term result, or the average of two short-term results, is 4 pCi/L or more.

What is the difference between a short-term and long-term radon test?

Short-term tests run from 2 to 90 days depending on the device. Long-term tests run from 91 days to 12 months and give a better picture of your year-round average, since radon changes with the seasons.

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

Divide by 37. EPA's 4 pCi/L action level is about 150 Bq/m3, and WHO's 100 Bq/m3 reference level is about 2.7 pCi/L.

Radon Test Results: What Your Number Means and What to Do

Your radon test result: what it means and what to do next

EPA recommends fixing a home at 4 pCi/L or higher and considering a fix from 2 to 4. Before you hire anyone, check one thing: was this a single short-term test? If so, the next step is usually a confirming test, not a contractor.

Check your number

Your result

Unit

Kind of test

Enter a number to see what EPA guidance says.

Logic follows EPA's action level and the EPA/California follow-up testing guidance cited below. 1 pCi/L = 37 Bq/m³.

What the number means

Below 2 pCi/L

Low, but not zero risk

The average US home is about 1.3 pCi/L and outdoor air about 0.4. EPA says there is no known safe level. Retest every 2 to 5 years and after renovating or finishing a basement.

Source: EPA, What is EPA's action level for radon?; California Department of Public Health, Radon Testing. Checked 2026-11-05.

2 to 3.9 pCi/L

Consider fixing

EPA recommends considering a fix in this range. The World Health Organization's suggested reference level is 2.7 pCi/L (100 Bq/m³). If this was a single short-term test, a long-term test gives a better yearly picture.

Source: EPA, What is EPA's action level for radon?; EPA, Does WHO's 2009 recommendation affect EPA's action level?; California Department of Public Health, Radon Testing. Checked 2026-11-05.

4 pCi/L or higher

EPA recommends fixing

EPA's action level is 4 pCi/L (about 150 Bq/m³). If your number came from one short-term test, confirm it first: fix if a long-term test, or the average of two short-term tests, is 4 or more.

Source: EPA, What is EPA's action level for radon?; EPA radon testing worksheet (EPA 402-B-19-060); California Department of Public Health, Radon Testing. Checked 2026-11-05.

Short-term vs. long-term tests

Short-term tests run 2 to 90 days depending on the device, and most kits are a few days. Long-term tests run 91 days to a year. Radon rises and falls with the seasons, so a long-term test is the better picture of what you actually breathe; a short-term test is a fast first look. If two short-term tests disagree, EPA's worksheet averages them.

Make sure the test was done right

On the lowest level you use, about 20 inches off the floor and at least a foot below the ceiling.

At least 3 feet from outside doors and windows, out of damp rooms like laundry rooms and bathrooms, and not right above or below an HVAC vent.

For a short-term test, keep windows and doors closed (except normal coming and going) for 12 hours before and during the test.

If you need to fix it

Find a state-credentialed installer: Iowa, Nebraska, Colorado, Kansas.

Check their license on your state's own lookup before you sign.

Get more than one quote and compare them with our 8-question checklist. See what mitigation really costs.

Retest after it's installed: no sooner than 24 hours and within 30 days. Then retest every two years.

Buying or selling? What each state requires sellers to disclose is on our radon laws by state page.