Radon Levels by State 2025
Average Radon Level (pCi/L)
2.0
4.0
6.0
8.0
10.0
State | Average Radon Level (pCi/L)↓ | |
|---|---|---|
 | Alaska | 10.7 |
 | South Dakota | 9.6 |
 | Pennsylvania | 8.6 |
 | Ohio | 7.8 |
 | Washington | 7.5 |
 | Kentucky | 7.4 |
 | Montana | 7.4 |
 | Idaho | 7.3 |
 | Colorado | 6.8 |
 | Iowa | 6.1 |
 | West Virginia | 6.1 |
 | North Dakota | 6.0 |
 | Maine | 5.9 |
 | Wisconsin | 5.7 |
 | New Hampshire | 5.6 |
 | Maryland | 5.4 |
 | Illinois | 5.3 |
 | Nebraska | 5.2 |
 | Wyoming | 5.0 |
 | Kansas | 4.9 |
 | Tennessee | 4.8 |
 | Indiana | 4.7 |
 | Minnesota | 4.6 |
 | New Jersey | 4.4 |
 | Utah | 4.4 |
 | Missouri | 4.3 |
 | Rhode Island | 4.3 |
 | New York | 4.2 |
 | North Carolina | 4.0 |
 | Alabama | 3.9 |
 | Massachusetts | 3.9 |
 | New Mexico | 3.9 |
 | Vermont | 3.7 |
 | Virginia | 3.6 |
 | Michigan | 3.5 |
 | Connecticut | 3.4 |
 | Nevada | 3.4 |
 | Oregon | 3.1 |
 | Arkansas | 2.5 |
 | Oklahoma | 2.5 |
 | Delaware | 2.4 |
 | South Carolina | 2.4 |
 | California | 2.3 |
 | Georgia | 2.3 |
 | Texas | 2.1 |
 | Arizona | 1.9 |
 | Florida | 1.8 |
 | District of Columbia | 1.6 |
 | Mississippi | 1.2 |
 | Louisiana | 1.1 |
- Radon levels shown are state-level averages. Within each state, the radon level can vary significantly from one county, municipality, or home site to another.
- Radon levels are measured in picocuries per liter (pCi/L). One pCi/L represents one trillionth of a curie of radioactivity per liter of air.
Radon is a naturally occurring radioactive gas that is odorless, tasteless, and colorless. The natural radioactive decay of uranium forms it in rock, soil, and water.
Radon is the second-leading cause of lung cancer, costing the United States over $2 billion per year in both direct and indirect healthcare costs. Radon has no immediate symptoms that will alert someone of its presence, and it takes years of exposure before any problems become apparent.
According to the US EPA, nearly 1 in 3 homes checked in seven states had radon levels over the recommended action level for radon exposure of 4 pCi/L. The pCi in “pCi/L” is a picocurie, which is one-trillionth of a curie and measures the rate of radioactive decay of radon. At 4 pCi/L, there will be approximately 12,672 disintegrations in one liter of air during a 24-hour period.
Top 10 States with the Highest Radon Levels
State | Average Radon Level (pCi/L) |
|---|---|
| Alaska | 10.7 |
| South Dakota | 9.6 |
| Pennsylvania | 8.6 |
| Ohio | 7.8 |
| Washington | 7.5 |
| Kentucky | 7.4 |
| Montana | 7.4 |
| Idaho | 7.3 |
| Colorado | 6.8 |
| Iowa | 6.1 |
According to Air Chek, Inc., 31 states have radon exposure above 4 pCi/L. In general, these states are in the northern half of the United States. Only five states and the District of Columbia are considered to have low radon levels. Those states are:
- Arizona
- Florida
- District of Columbia
- Mississippi
- Louisiana
- Hawaii
Hawaii has the lowest radon levels of all 50 states, with an average level of 0 pCi/L. The uranium content of Hawaiian rocks is low, and most rocks near the surface are porous, allowing for air infiltration to dilute radon. Alaska has the highest radon levels of 10.7 pCi/L. Homeowners in Alaska are encouraged to test for radon every two years.
