Radon levels in Maryland: Low
The model predicts a population-weighted basement average of 1.3 pCi/L (model estimate) across Maryland's 24 counties - about 28% below the US average of 1.8 pCi/L. Above-ground floors average 1.0 pCi/L.
Predicted (model estimate). The pCi/L figures on this page are long-term area averages from a peer-reviewed national model built on millions of real radon tests (2001-2021). They describe the typical home in this area - not your home, which can be several times higher or lower. The EPA radon zone is a separate, 1993 county-level classification. How the numbers work.
8 / 24
EPA Zone 1 counties (33%)
9 / 7
Zone 2 / Zone 3 counties
0
counties predicted ≥ 4 pCi/L
0%
of ZIP codes predicted ≥ 4 pCi/L
Test Maryland once anyway - radon varies house to house
The predicted basement average here is 1.3 pCi/L, below the EPA's 2 pCi/L "consider fixing" threshold. That's good news for the area - but the EPA still recommends every home be tested, because foundation cracks, soil pockets and ventilation make one house very different from its neighbor. One inexpensive kit settles it.
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What the data says about radon in Maryland
On the EPA's 1993 radon zone map, 8 of Maryland's 24 counties are EPA Zone 1 (33%), 9 are Zone 2 and 7 are Zone 3. Zone 2 (predicted screening average of 2-4 pCi/L) is the most common designation, with the 8 Zone 1 counties marking where the EPA expected the highest potential. That classification has not been revised since 1993; it describes counties, not homes, and elevated readings turn up in Zone 3 counties every year.
Maryland models out at 1.3 pCi/L predicted basement average (low; 28% below the US average of 1.8). Of the 24 counties with predictions, 0 are predicted at or above 4 pCi/L, 3 in the 2-4 band and 21 below 2. The highest predicted county is Washington County at 2.9 pCi/L; the lowest is Baltimore city at 1.0 - a 1.9 pCi/L spread that means a statewide average tells you little about any one county.
At ZIP-code resolution, 0% of Maryland ZIPs are predicted at 4 pCi/L or higher in the basement and 10.1% at 2 or higher - below the national shares of 4.2% and 48.7%. No ZIP in the state is predicted above 4 on average - but averages hide individual homes, which is why the EPA still asks everyone to test.
Maryland counties by predicted radon
Sorted highest to lowest predicted basement average (model estimate). 24 counties.
| County | Predicted basement | Upstairs | Grade | EPA zone | ZIPs |
|---|---|---|---|---|---|
| Washington County | 2.9 pCi/L | 2.1 | Moderate | EPA Zone 1 | 14 |
| Allegany County | 2.6 pCi/L | 1.6 | Moderate | EPA Zone 2 | 8 |
| Garrett County | 2.5 pCi/L | 1.3 | Moderate | EPA Zone 2 | 11 |
| Carroll County | 1.8 pCi/L | 1.6 | Low | EPA Zone 1 | 9 |
| Calvert County | 1.6 pCi/L | 1.3 | Low | EPA Zone 1 | 12 |
| Cecil County | 1.5 pCi/L | 1.1 | Low | EPA Zone 2 | 13 |
| Frederick County | 1.5 pCi/L | 1.3 | Low | EPA Zone 1 | 24 |
| Caroline County | 1.4 pCi/L | 0.7 | Low | EPA Zone 3 | 7 |
| Kent County | 1.4 pCi/L | 0.8 | Low | EPA Zone 3 | 9 |
| St. Mary's County | 1.4 pCi/L | 1.0 | Low | EPA Zone 2 | 22 |
| Talbot County | 1.4 pCi/L | 0.8 | Low | EPA Zone 3 | 13 |
| Queen Anne's County | 1.4 pCi/L | 0.7 | Low | EPA Zone 3 | 12 |
| Charles County | 1.4 pCi/L | 0.9 | Low | EPA Zone 2 | 21 |
| Worcester County | 1.4 pCi/L | 0.6 | Low | EPA Zone 3 | 9 |
| Dorchester County | 1.4 pCi/L | 0.7 | Low | EPA Zone 3 | 14 |
| Somerset County | 1.4 pCi/L | 0.7 | Low | EPA Zone 2 | 6 |
| Wicomico County | 1.3 pCi/L | 0.6 | Low | EPA Zone 3 | 15 |
| Harford County | 1.3 pCi/L | 1.0 | Low | EPA Zone 1 | 18 |
| Howard County | 1.2 pCi/L | 1.0 | Low | EPA Zone 1 | 19 |
| Prince George's County | 1.2 pCi/L | 0.9 | Low | EPA Zone 2 | 34 |
| Anne Arundel County | 1.2 pCi/L | 0.9 | Low | EPA Zone 2 | 35 |
| Montgomery County | 1.2 pCi/L | 0.9 | Low | EPA Zone 1 | 42 |
| Baltimore County | 1.1 pCi/L | 0.9 | Low | EPA Zone 1 | 37 |
| Baltimore city | 1.0 pCi/L | 0.8 | Low | EPA Zone 2 | 20 |
Radon levels in Maryland cities
The 20 most-populous Maryland places among the 1,000 largest US cities (Census incorporated places and CDPs), by population. City figures are ZIP-land-weighted means of the model's ZIP predictions (model estimate).
| City | Population | Predicted basement | Upstairs | Grade | ZIPs ≥ 4 |
|---|---|---|---|---|---|
| Baltimore | 565,239 | 1.0 pCi/L | 0.8 | Low | 0% |
| Columbia | 99,615 | 1.1 pCi/L | 1.0 | Low | 0% |
| Germantown | 86,395 | 1.1 pCi/L | 1.0 | Low | 0% |
| Frederick | 85,793 | 1.1 pCi/L | 1.3 | Low | 0% |
| Silver Spring | 71,452 | 1.4 pCi/L | 0.9 | Low | 0% |
| Gaithersburg | 69,563 | 1.0 pCi/L | 0.8 | Low | 0% |
| Waldorf | 67,752 | 1.4 pCi/L | 0.9 | Low | 0% |
| Glen Burnie | 67,639 | 1.1 pCi/L | 0.8 | Low | 0% |
| Rockville | 67,297 | 1.0 pCi/L | 0.8 | Low | 0% |
| Ellicott City | 65,834 | 1.4 pCi/L | 1.1 | Low | 0% |
| Dundalk | 63,597 | 0.7 pCi/L | 0.7 | Low | 0% |
| Bethesda | 60,858 | 1.1 pCi/L | 0.8 | Low | 0% |
| Bowie | 57,254 | 1.3 pCi/L | 1.1 | Low | 0% |
| Towson | 55,197 | 1.3 pCi/L | 1.0 | Low | 0% |
| Aspen Hill | 48,759 | 1.2 pCi/L | 0.9 | Low | 0% |
| Wheaton | 48,284 | 1.2 pCi/L | 0.9 | Low | 0% |
| Bel Air South | 47,709 | 1.1 pCi/L | 1.0 | Low | 0% |
| Potomac | 44,965 | 1.2 pCi/L | 0.9 | Low | 0% |
| Severn | 44,231 | 1.1 pCi/L | 0.8 | Low | 0% |
| North Bethesda | 43,828 | 1.2 pCi/L | 0.8 | Low | 0% |
Highest-radon ZIP codes in Maryland
The 10 Maryland ZIP codes with the highest predicted basement average (model estimate), out of 424 modeled. A ZIP average is still an area figure - neighboring homes routinely test several pCi/L apart.
| ZIP | County | Predicted basement | Upstairs | Grade |
|---|---|---|---|---|
| 21722 | Washington County | 3.6 pCi/L | 2.2 | Moderate |
| 21711 | Washington County | 3.4 pCi/L | 1.7 | Moderate |
| 21750 | Washington County | 3.4 pCi/L | 1.8 | Moderate |
| 21795 | Washington County | 3.3 pCi/L | 2.1 | Moderate |
| 21742 | Washington County | 3.2 pCi/L | 2.3 | Moderate |
| 21782 | Washington County | 3.2 pCi/L | 2.2 | Moderate |
| 21530 | Allegany County | 3.1 pCi/L | 1.4 | Moderate |
| 21555 | Allegany County | 3.0 pCi/L | 1.4 | Moderate |
| 21767 | Washington County | 3.0 pCi/L | 1.9 | Moderate |
| 21766 | Allegany County | 2.9 pCi/L | 1.4 | Moderate |
Maryland radon questions
- Is radon high in Maryland?
- Maryland's population-weighted predicted basement average is 1.3 pCi/L, about 28% below the US average of 1.8. 0 of its 24 modeled counties are predicted at or above the EPA action level of 4 pCi/L, 3 are in the 2-4 "consider fixing" range and 21 are below 2. 0% of Maryland ZIP codes are predicted at 4 or higher.
- Which Maryland county has the highest radon?
- Washington County has the highest predicted basement average in Maryland at 2.9 pCi/L (EPA Zone 1). The lowest is Baltimore city at 1.0 pCi/L. These are area figures; individual homes in any county can test far higher.
- How many EPA Zone 1 counties are in Maryland?
- 8 of Maryland's 24 counties (33%) are EPA Zone 1 (highest potential), 9 are Zone 2 and 7 are Zone 3. The EPA zone map dates from 1993; the predicted values on this page come from a 2001-2021 model built on millions of actual tests, so the two can disagree for a given county.
- Should I test for radon in Maryland?
- Yes. Even though Maryland's predicted average is below 2 pCi/L, the EPA recommends every home be tested - radon varies house to house, and 10.1% of Maryland ZIP codes are still predicted at 2 pCi/L or higher.
Maryland radon program
Maryland's radon program page is at mde.maryland.gov; it lists testing and certified-mitigator guidance for the state. The EPA also keeps a directory of every state radon contact: EPA state radon contacts page. Then read how to test and what mitigation costs.