Radon levels by state, ranked
All 50 states and DC ranked by predicted basement radon - the population-weighted average of every county's model estimate - with the share of EPA Zone 1 counties and how many counties sit at or above the 4 pCi/L action level. The US population-weighted average is 1.8 pCi/L; 0 states average above 4 and 22 above 2.
Highest: South Dakota (3.9), Nebraska (3.6), Iowa (3.5), North Dakota (3.3), Montana (3.1). Lowest: District of Columbia (1.1), Florida (1.3), Maryland (1.3), New Jersey (1.3), Delaware (1.3). Alaska and Hawaii are outside the model and are listed last with EPA zones only. 6 states (Idaho, Minnesota, New York, Pennsylvania, Vermont, Wisconsin) also publish measured county test results, shown on their state and county pages and marked in the table.
Predicted (model estimate). Values are long-term area averages from the 2001-2021 National Radon Exposure Model (Harvard/Emory, CC0), not test results, and describe the typical home in a state - not any specific house. See the methodology.
| # | State | Predicted basement | Upstairs | Grade | Zone 1 counties | Counties ≥ 4 | ZIPs ≥ 4 | Highest county | Measured data |
|---|---|---|---|---|---|---|---|---|---|
| 1 | South Dakota | 3.9 pCi/L | 2.2 | Moderate | 48 / 66 (73%) | 34 / 66 | 42.1% | Jerauld 5.2 | - |
| 2 | Nebraska | 3.6 pCi/L | 2.1 | Moderate | 53 / 93 (57%) | 42 / 93 | 50.1% | Burt 5.7 | - |
| 3 | Iowa | 3.5 pCi/L | 2.1 | Moderate | 99 / 99 (100%) | 50 / 99 | 41% | Sioux 6.3 | - |
| 4 | North Dakota | 3.3 pCi/L | 2.1 | Moderate | 53 / 53 (100%) | 11 / 53 | 11.7% | Grand Forks 4.4 | - |
| 5 | Montana | 3.1 pCi/L | 2.1 | Moderate | 49 / 56 (88%) | 1 / 56 | 1% | Park 4.2 | - |
| 6 | Wyoming | 3.0 pCi/L | 2.1 | Moderate | 21 / 23 (91%) | 1 / 23 | 2.9% | Lincoln 4.1 | - |
| 7 | Ohio | 2.8 pCi/L | 1.6 | Moderate | 53 / 88 (60%) | 14 / 88 | 10.7% | Knox 5.8 | - |
| 8 | Idaho | 2.6 pCi/L | 1.7 | Moderate | 19 / 44 (43%) | 2 / 44 | 3.3% | Teton 4.4 | through 2019 (start year not stated by the source), 37.2% ≥ 4 |
| 9 | Colorado | 2.6 pCi/L | 2.0 | Moderate | 53 / 64 (83%) | 3 / 64 | 1.8% | Pueblo 4.2 | - |
| 10 | Kansas | 2.6 pCi/L | 1.6 | Moderate | 65 / 105 (62%) | 25 / 105 | 16.5% | Jewell 4.7 | - |
| 11 | Kentucky | 2.5 pCi/L | 1.5 | Moderate | 30 / 120 (25%) | 0 / 120 | 0.6% | Jessamine 3.7 | - |
| 12 | Minnesota | 2.4 pCi/L | 1.7 | Moderate | 68 / 87 (78%) | 9 / 87 | 8.6% | Rock 4.7 | 2016-2025 |
| 13 | West Virginia | 2.4 pCi/L | 1.4 | Moderate | 20 / 55 (36%) | 0 / 55 | 0.2% | Morgan 3.7 | - |
| 14 | Tennessee | 2.3 pCi/L | 1.4 | Moderate | 39 / 95 (41%) | 0 / 95 | 0.2% | Sullivan 3.2 | - |
| 15 | Indiana | 2.3 pCi/L | 1.4 | Moderate | 57 / 92 (62%) | 0 / 92 | 0.1% | Blackford 3.5 | - |
| 16 | Pennsylvania | 2.3 pCi/L | 1.5 | Moderate | 49 / 67 (73%) | 2 / 67 | 2.9% | Lebanon 4.8 | 1988-2026, 33.2% ≥ 4 |
| 17 | Utah | 2.3 pCi/L | 1.5 | Moderate | 7 / 29 (24%) | 0 / 29 | 1.3% | Wasatch 3.9 | - |
| 18 | Missouri | 2.2 pCi/L | 1.3 | Moderate | 11 / 115 (10%) | 1 / 115 | 1.3% | Atchison 4.4 | - |
| 19 | Maine | 2.2 pCi/L | 1.2 | Moderate | 12 / 16 (75%) | 0 / 16 | 0% | Oxford 2.6 | - |
| 20 | New Mexico | 2.1 pCi/L | 1.5 | Moderate | 7 / 33 (21%) | 0 / 32 | 0% | Taos 2.9 | - |
| 21 | New Hampshire | 2.1 pCi/L | 1.3 | Moderate | 1 / 10 (10%) | 0 / 10 | 0.4% | Carroll 2.3 | - |
| 22 | Wisconsin | 2.0 pCi/L | 1.4 | Moderate | 28 / 72 (39%) | 0 / 72 | 0.1% | Lafayette 3.4 | 1995-2016, 28.8% ≥ 4 |
| 23 | Nevada | 1.9 pCi/L | 1.1 | Low | 9 / 17 (53%) | 0 / 17 | 0% | White Pine 3.0 | - |
| 24 | Illinois | 1.9 pCi/L | 1.2 | Low | 56 / 102 (55%) | 1 / 102 | 0.4% | Knox 4.0 | - |
| 25 | Georgia | 1.9 pCi/L | 1.0 | Low | 4 / 159 (3%) | 0 / 159 | 0% | Walton 2.8 | - |
| 26 | Massachusetts | 1.8 pCi/L | 1.1 | Low | 3 / 14 (21%) | 0 / 14 | 0.4% | Worcester 2.5 | - |
| 27 | Alabama | 1.8 pCi/L | 1.1 | Low | 13 / 67 (19%) | 0 / 67 | 0% | Clay 2.9 | - |
| 28 | Oklahoma | 1.8 pCi/L | 0.9 | Low | 0 / 77 (0%) | 0 / 77 | 0% | Cimarron 2.5 | - |
| 29 | Arkansas | 1.8 pCi/L | 0.9 | Low | 0 / 75 (0%) | 0 / 75 | 0% | Boone 2.3 | - |
| 30 | Arizona | 1.7 pCi/L | 1.0 | Low | 0 / 15 (0%) | 0 / 15 | 0% | Coconino 2.3 | - |
| 31 | Oregon | 1.7 pCi/L | 0.9 | Low | 0 / 36 (0%) | 0 / 36 | 0% | Union 2.5 | - |
| 32 | Vermont | 1.7 pCi/L | 1.0 | Low | 0 / 14 (0%) | 0 / 14 | 0% | Bennington 2.0 | 1994-2025, 15.2% ≥ 4 |
| 33 | North Carolina | 1.7 pCi/L | 0.9 | Low | 8 / 100 (8%) | 0 / 100 | 0.3% | Transylvania 3.6 | - |
| 34 | Virginia | 1.6 pCi/L | 1.0 | Low | 62 / 133 (47%) | 0 / 112 | 0.1% | Wythe 3.3 | - |
| 35 | South Carolina | 1.6 pCi/L | 0.9 | Low | 1 / 46 (2%) | 0 / 46 | 0% | Oconee 2.5 | - |
| 36 | Michigan | 1.6 pCi/L | 1.0 | Low | 9 / 83 (11%) | 0 / 83 | 0% | Branch 3.5 | - |
| 37 | Washington | 1.6 pCi/L | 0.8 | Low | 7 / 39 (18%) | 0 / 39 | 0% | Pend Oreille 3.1 | - |
| 38 | Rhode Island | 1.6 pCi/L | 0.9 | Low | 2 / 5 (40%) | 0 / 5 | 0% | Washington 2.5 | - |
| 39 | Texas | 1.5 pCi/L | 0.8 | Low | 0 / 254 (0%) | 0 / 253 | 0% | Hemphill 2.5 | - |
| 40 | Connecticut | 1.5 pCi/L | 1.0 | Low | 4 / 8 (50%) | 0 / 8 | 0% | Windham 2.0 | - |
| 41 | California | 1.5 pCi/L | 0.9 | Low | 2 / 58 (3%) | 0 / 58 | 0% | Mono 2.7 | - |
| 42 | Mississippi | 1.5 pCi/L | 0.9 | Low | 0 / 82 (0%) | 0 / 82 | 0% | Alcorn 1.8 | - |
| 43 | Louisiana | 1.4 pCi/L | 0.7 | Low | 0 / 64 (0%) | 0 / 64 | 0% | Beauregard Parish 1.6 | - |
| 44 | New York | 1.4 pCi/L | 0.8 | Low | 34 / 62 (55%) | 0 / 62 | 0% | Schuyler 2.8 | 1987-2025, 29.9% ≥ 4 |
| 45 | Delaware | 1.3 pCi/L | 0.8 | Low | 0 / 3 (0%) | 0 / 3 | 0% | Sussex 1.4 | - |
| 46 | New Jersey | 1.3 pCi/L | 0.8 | Low | 7 / 21 (33%) | 0 / 21 | 0% | Warren 2.3 | - |
| 47 | Maryland | 1.3 pCi/L | 1.0 | Low | 8 / 24 (33%) | 0 / 24 | 0% | Washington 2.9 | - |
| 48 | Florida | 1.3 pCi/L | 1.0 | Low | 0 / 67 (0%) | 0 / 67 | 0% | Jefferson 1.6 | - |
| 49 | District of Columbia | 1.1 pCi/L | 0.8 | Low | 0 / 1 (0%) | 0 / 1 | 0% | District of Columbia 1.1 | - |
| - | Alaska | not modeled | - | zone only | 0 / 30 (0%) | - | - | - | - |
| - | Hawaii | not modeled | - | zone only | 0 / 5 (0%) | - | - | - | - |
How to read this table
Predicted basement is the state's counties' model estimates weighted by 2010 ZIP population, so it describes where people live, not land area; the grade uses the EPA thresholds (High ≥ 4, Moderate 2-4, Low < 2). Zone 1 counties is from the EPA's 1993 map and is a count of counties, so a large rural state can rank high on Zone 1 share while its population-weighted average is moderate. Counties ≥ 4 counts counties whose predicted basement mean is at or above the action level, out of counties with a prediction. Measured data marks states whose health department publishes county-level test results; the percentage is the test-weighted share of results at or above 4 pCi/L, which runs higher than model averages because tests are voluntary and basement-heavy.
A high-ranking state does not make every home in it high, and a low-ranking state does not make yours safe: 1,220 ZIP codes nationally are predicted at 4 pCi/L or above, and elevated homes are found in every state. Use the ranking to decide how urgently to test, then trust the test.
Radon by state: quick answers
- Which state has the highest radon levels?
- South Dakota has the highest population-weighted predicted basement average at 3.9 pCi/L, followed by Nebraska (3.6), Iowa (3.5), North Dakota (3.3), Montana (3.1). These are model estimates of long-term area averages from the 2001-2021 National Radon Exposure Model, not statewide test results.
- Which state has the lowest radon levels?
- District of Columbia has the lowest predicted basement average at 1.1 pCi/L, then Florida (1.3), Maryland (1.3), New Jersey (1.3), Delaware (1.3). Alaska and Hawaii are not covered by the model; Alaska is 0 Zone 1 / 5 Zone 2 / 25 Zone 3 and Hawaii is entirely Zone 3 on the EPA map.
- How many states average above the EPA action level?
- 0 of the 49 modeled states have a population-weighted predicted basement average at or above 4 pCi/L, and 22 are at or above 2 pCi/L. The US population-weighted average is 1.8 pCi/L. Averages describe the typical home; 1,220 ZIP codes nationwide are predicted at 4 or higher regardless of their state's rank.
- Is the EPA zone map the same as this ranking?
- No. The EPA map (1993) classifies counties into three zones; Iowa, North Dakota are entirely Zone 1, 13 states have no Zone 1 county (Alaska, Arizona, Arkansas, Delaware, District of Columbia, Florida, Hawaii, Louisiana, Mississippi, Oklahoma, Oregon, Texas, Vermont). The ranking here uses a 2001-2021 model built on millions of tests, so a state's Zone 1 share and its predicted average can disagree.
Download the underlying tables on the Data & Downloads page · Why basement and upstairs numbers differ