Radon levels: what your number means, from safe to high

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• Test16 min read

  Radon limits: EPA's action level, WHO's reference level and what counts as acceptableThe radon limits people search for are guidance levels, not a line between safe and unsafe: EPA recommends fixing a home at 4 pCi/L (about 148 Bq/m3) and considering a fix from 2 pCi/L, and WHO recommends a national reference level of 100 Bq/m3, at most 300 Bq/m3.Read the guide

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  Radon inspection: how a professional radon test works, what it proves and whether it is worth itA radon inspection is a radon test run by a qualified tester, who places a device on the lowest level of the home that could be used regularly and runs it for a minimum of 48 hours under closed-house conditions.Read the guide

• Learn22 min read

  Radon lung cancer risk: what the evidence shows and what lowers itRadon is the second leading cause of lung cancer in the United States after smoking, and EPA estimates it is responsible for about 21,000 lung cancer deaths a year, about 2,900 among people who have never smoked.Read the guide

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  EPA radon guidance: action level, map and guidesEPA sets the 4 pCi/L radon action level, publishes the Map of Radon Zones and its radon guides, and says all homes should be tested for radon.Read the guide

Radon levels describe how much radon is in a building's air. In the United States a test reports the result in picocuries per liter, pCi/L, a unit of the radioactivity in a liter of air; most other countries use becquerels per cubic meter, Bq/m3. Testing is the only way to know the radon level in a specific building.

4 pCi/L

EPA's action level, about 150 Bq/m3: the point at which EPA recommends fixing a home.

2 to 4 pCi/L

The range where EPA recommends considering a fix.

No level is safe

Any radon exposure carries some risk, so lower is always better.

Read moreA paragraph and a figure, 1 min

Two numbers frame every result. 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. Neither is a line between safe and unsafe: any radon exposure carries some risk, and you can reduce your risk of lung cancer by lowering your radon level. The rest of this page puts your number in context. If you already have a result, the interpreter reads it for you.

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2 pCi/L

4 pCi/L

00 Bq/m³274 Bq/m³4148 Bq/m³6222 Bq/m³8296 Bq/m³10+370 Bq/m³

• 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.

EPA's risk chart is the closest thing to an official radon level chart. For each level it gives the Bq/m3 equivalent, an estimate of how many people out of 1,000 could get lung cancer if exposed to that level over a lifetime, for people who smoked and for people who never smoked, and what to do. These are population estimates from a 2003 risk assessment, not a prediction for any one person.

There is none. Any radon exposure carries some risk and no level of radon is safe, and because there is no known safe level of exposure, EPA also recommends considering a fix between 2 and 4 pCi/L. The 4 pCi/L action level is the point at which EPA recommends fixing, not a safety threshold.

1.3 pCi/L

Average indoor radon level in U.S. homes (50 Bq/m3), according to EPA

0.4 pCi/L

Average U.S. outdoor radon level (15 Bq/m3), about one tenth of EPA's action level

Nearly one in 15

U.S. homes with an elevated level, 4 pCi/L or more, by EPA's estimate.

The national Map of Radon Zones gives every county a predicted radon potential, not a measurement. The zones are defined by the average indoor level a home in the area may have:

Where you measure matters. Radon levels are usually higher in basements, cellars and living spaces in contact with the ground, but considerable radon concentrations can also be found above the ground floor. That is why a test goes in the lowest lived-in level: the basement if it is used often, otherwise the first floor.

A working system usually brings a home well under the action level. Radon levels in most homes can be reduced to 2 pCi/L or below with today's technology. Every system should get the level below the 4 pCi/L action level, and a quality system may bring year-round levels below 2 pCi/L. Many contractors guarantee to reach a negotiated level, such as 2 pCi/L or less.

Other countries set their own figure, usually called a reference level. WHO recommends that national reference levels be set at 100 Bq/m3 (2.7 pCi/L) if possible, and not above 300 Bq/m3 (8.1 pCi/L). That does not directly change the U.S. 4 pCi/L (150 Bq/m3) action level, because EPA has long also recommended considering a fix from 2 pCi/L and holds that there is no known safe level.

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• U.S. EPA
• World Health Organization

0100200300 Bq/m³

• EPA: average indoor air48.1 Bq/m³ (1.3 pCi/L)The average for indoor air is 48.1 Bq/m3 (1.3 pCi/L).
• EPA: consider fixing2 pCi/L (74 Bq/m³, calculated)Consider fixing between 2 and 4 pCi/L.
• WHO: reference level100 Bq/m³ (2.7 pCi/L, calculated)A national annual average residential radon concentration reference level of 100 Bq/m3.
• EPA: fix your home148 Bq/m³ (4 pCi/L)EPA recommends fixing your home when the radon level is at or above 148 Bq/m3 (4 pCi/L).
• WHO: upper limit for a reference level300 Bq/m³ (8.1 pCi/L, calculated)If 100 Bq/m3 cannot be reached under the prevailing country-specific conditions, the reference level should not exceed 300 Bq/m3.

Calculated by Radon411: figures marked calculated convert the publisher's unit at 37 Bq/m³ per pCi/L, EPA's factor: “1 pCi/L corresponds to 37 Bq/m3”. A becquerel is one atomic nucleus transforming each second. WHO sets reference levels for countries; EPA's level is a recommendation to fix a home.

Show the whole figure

U.S. results are reported in pCi/L, with the Bq/m3 equivalent printed beside the key figures. The pairs below are the published ones. The general rule, about 37 Bq/m3 to 1 pCi/L, is our calculation from the published figure of 148 Bq/m3 for 4 pCi/L, which is also rounded to 150 Bq/m3.