--- title: What Does pCi/L Mean for Radon? canonical: "https://radonmitigationyorkpa.net/radon-guide/what-is-pci-l/" pubDate: "2026-10-01T00:00:00.000Z" updatedDate: "2026-10-03T00:18:00.000Z" author: Radon Mitigation York PA description: "pCi/L means picocuries per liter, the unit for radon in air. Learn what the number counts, how it converts to Bq/m3 and what 4.0 pCi/L means." --- # What Does pCi/L Mean for Radon? pCi/L stands for picocuries per liter. It is the unit used in the U.S. to measure radon in air. It counts radioactive decay in one liter of air. One picocurie is about 2.2 atoms breaking down each minute, so 4 pCi/L means roughly 9 radon atoms decaying every minute in each liter. Local results, like [York County radon readings in pCi/L](/york-county-radon-levels/), use the same unit. ## Breaking down the unit The unit has two parts. **Picocurie (pCi).** A curie is a unit of radioactivity. "Pico" means one trillionth. So a picocurie is a very small amount of radioactivity. It works out to about 2.2 radioactive decays per minute. **Per liter (L).** A liter is about the size of a large water bottle. The number tells you how much radon activity is in each liter of air in your home. Put together, a radon result of 4.0 pCi/L means each liter of air has about 4 picocuries of radon activity. ## A simple way to picture it Think of a room full of air. In a basement at 4 pCi/L, every liter of that air has roughly 9 radon atoms breaking down each minute. A typical basement holds tens of thousands of liters of air, so that adds up to a lot of tiny radiation events every minute, all day, every day. Those events are invisible and silent. You can't feel them. That is why radon has to be measured with a test device. ## Common radon numbers in pCi/L | Level | What it is | |---|---| | 0.4 pCi/L | Average outdoor air (EPA) | | 1.3 pCi/L | Average U.S. indoor air (EPA) | | 2.0 pCi/L | Start of EPA's "consider fixing" range | | 4.0 pCi/L | EPA action level: fix your home | Source: [EPA's Citizen's Guide to Radon](https://www.epa.gov/sites/default/files/2016-12/documents/2016_a_citizens_guide_to_radon.pdf). In York County, many results land above 4.0. PA DEP's test data shows about half of county tests at or above that mark. ## pCi/L vs. Bq/m3 Most other countries measure radon in becquerels per cubic meter (Bq/m3). One becquerel is one atom decaying per second. The conversion is simple: - **1 pCi/L = 37 Bq/m3** - **4 pCi/L = about 148 Bq/m3** (EPA often rounds this to 150) - **100 Bq/m3 = about 2.7 pCi/L** So if you read about radon from Canada, Europe or the World Health Organization, multiply pCi/L by 37 to compare. ## What about WL (working levels)? Some older reports use working levels (WL). WL measures radon's decay products rather than the gas itself. You'll rarely see it on a modern home test. If you do, ask the testing company to explain how it relates to pCi/L, since the conversion depends on conditions in the house. ## Why the unit matters for your decisions Knowing the unit helps you read a test report with confidence: - **Look for the average.** A professional continuous monitor gives hourly readings and an overall average. The average is the number to compare to EPA's 4.0 action level. - **Check the test location.** A basement result is usually higher than an upstairs result. - **Compare like with like.** Before and after numbers should come from the same spot and similar conditions. To understand where the gas itself comes from, read about [what radon is and where it comes from](/radon-guide/what-is-radon/). ## Key takeaways - pCi/L means picocuries per liter, the U.S. unit for radon in air. - One picocurie is about 2.2 atomic decays per minute. - EPA's action level is 4.0 pCi/L. Consider fixing from 2 to 4. - 1 pCi/L equals 37 Bq/m3. ## Frequently Asked Questions ### Is a higher pCi/L number always worse? Yes. Risk rises with the level. A result of 8 pCi/L carries about twice the long-term risk of 4 pCi/L. ### Why do my hourly readings jump around? Radon shifts with weather, wind, rain and how the house is used. That is normal. Focus on the average over the full test. ## See local radon numbers Curious how pCi/L results look across your area? Check our York County radon levels page, which lists PA DEP test data by ZIP code. To test or fix your home, call [(717) 356-3035](tel:+17173563035) any time.