Radon levels chart: what your test result means

Radon level chart (pCi/L and Bq/m³)

pCi/L is picocuries per liter, the unit used in the U.S. Bq/m³ is becquerels per cubic meter, used by the WHO and most other countries. 1 pCi/L = 37 Bq/m³. Bq/m³ values here are converted and rounded; the EPA rounds 4 pCi/L to 150 Bq/m³.

Scroll sideways to see the whole diagram.

2 to 4 pCi/L: EPA says consider fixing4 pCi/L and above: EPA says fix

What are acceptable (or safe) radon levels?

No one can promise you a safe number. The EPA and the CDC both say there’s no known safe level of radon, and that the lower you get your home, the lower your risk. “Acceptable” usually means below the EPA’s action level of 4 pCi/L, but that’s the point to act, not the line where the risk starts.

The EPA action level: 4 pCi/L

At 4 pCi/L or higher, the EPA recommends fixing your home. Its Citizen’s Guide puts the risk in plain numbers: if 1,000 people who never smoked lived with 4 pCi/L over a lifetime, about 7 could get lung cancer. If those 1,000 people were smokers, about 62 could.

If your result is at or above 4, see how radon mitigation systems work.

Radon between 2 and 4 pCi/L

I won’t tell you your home is fine if it’s between 2 and 4 pCi/L. It’s under the EPA’s action level, but the risk doesn’t start exactly at 4, and the EPA recommends considering a fix from 2 pCi/L.

If it was a short-term test, I’ll explain what the number means and when a second test or a long-term test makes sense (see how to test for radon). If it’s a space where your family spends a lot of time, it’s worth looking at a fix even if the result is under 4.

What to do after your result

The EPA’s Citizen’s Guide lays out the steps:

1. First short-term test at 4 pCi/L or higher: take a follow-up test.
2. Choose the follow-up: a long-term test gives a better picture of your year-round average; a second short-term test gives a faster answer. If the first result is more than twice the action level (above 8 pCi/L), take a second short-term test right away.
3. Decide: fix the home if the long-term result is 4 pCi/L or more, or if the average of the two short-term tests is 4 pCi/L or more.

Some state programs add their own guidance. The Virginia Department of Health, for example, recommends a second, long-term test if the first result is between 4.0 and 9.9 pCi/L. At 10 pCi/L or higher, it recommends a second short-term test, averaged with the first. Home sales follow their own protocols, so check what your tester uses.

Before I give a quote, I always ask where and how the home was tested. If the test is valid, I won’t tell you to ignore the result. And with a very high reading, I wouldn’t tell anyone to wait months to fix it.

Radon result checker

Enter your test result and what kind of test it was. You get the next step from the EPA’s testing guidance.

Which test is this?

My first test A follow-up test

How long did it run?

Short-term (2 to 90 days) Long-term (more than 90 days)

Result

pCi/LBq/m³

Check my result

This checker follows the EPA’s Citizen’s Guide to Radon. It doesn’t estimate your health risk or diagnose your home, and some states add their own steps. For a home sale, follow the protocol your tester uses. With a continuous monitor, enter the average for the whole test, not a single hourly reading. Nothing you enter is stored or sent.

How the checker works

It applies the EPA’s steps. A first short-term test below 4 pCi/L doesn’t call for a follow-up; at 4 or higher, take a follow-up test, and if it’s above 8 (twice the action level), take a second short-term test right away. After a long-term test, the EPA recommends fixing the home at 4 pCi/L or higher. After two short-term tests, it recommends considering a fix if their average is 4 or higher. At any result between 2 and 4, the EPA recommends considering a fix. Bq/m³ are converted with 1 pCi/L = 37 Bq/m³, and results are rounded to one decimal place in pCi/L before the checker compares them.

Interactive tool: Radon result checker. This tool works on the web page. Use it at belowthesill.com/radon/levels/#checker

See all tools and checklists

Why your radon level changes

It can vary quite a bit from season to season and even from day to day. It depends on the weather, on how much of a chimney effect your house has and on how you ventilate. In one basement in Ohio, we measured 2.4 pCi/L in a short-term test and 6.7 pCi/L at another time of year. That doesn’t mean every home goes up in winter. More on what drives it in radon in your basement.

If you want to know your exposure over the whole year, a long-term test is best, if you have the time for one. I wouldn’t take two separate readings and say a house follows a particular seasonal pattern.

Converting pCi/L and Bq/m³

To convert pCi/L to Bq/m³, multiply by 37. To go the other way, divide by 37.

• 5.8 pCi/L × 37 = 214.6 Bq/m³ (about 215)
• 200 Bq/m³ ÷ 37 = 5.4 pCi/L

If your home monitor or a European source gives results in Bq/m³, convert them before you compare them with the EPA’s numbers.