Understanding your radon test results: pCi/L, Bq/m³, action levels and next steps

You followed the instructions, mailed your kit, and now there's a number on a lab report. What does it actually mean, and what should you do? This guide walks through reading a radon result, the units, how EPA's guidance levels work, how they compare with international guidelines, and the next steps at each level.

Reading the lab report

A typical report includes:

• Your result, usually in picocuries per liter (pCi/L).
• Test dates and duration. Short-term tests run 2 to 90 days, long-term tests more than 90 days.
• Device type, such as charcoal canister, alpha track, electret, or continuous monitor.
• Where the test was placed, as you reported it.
• Notes on validity. A lab may flag a test if it arrived too late or the dates were missing.
• Margin of error or detection limit, on some reports.

Check that the dates and location are right. A result from a test that sat in the mail for a week may be flagged or less reliable.

The units

• pCi/L (picocuries per liter) is the U.S. unit. It measures radioactivity per liter of air.
• Bq/m³ (becquerels per cubic meter) is used in most other countries.
• Conversion: 1 pCi/L = 37 Bq/m³. So 4 pCi/L ≈ 150 Bq/m³, and 2 pCi/L ≈ 75 Bq/m³.

Some professional reports also give working levels (WL), a measure of radon decay products. Most homeowners can ignore WL and focus on pCi/L.

What the numbers mean

For context, EPA reports that the average indoor radon level in U.S. homes is about 1.3 pCi/L, and the average outdoor level about 0.4 pCi/L.

EPA's guidance is:

• 4 pCi/L or higher: fix your home (after confirming with a follow-up test).
• 2 to 4 pCi/L: consider fixing your home.
• Below 2 pCi/L: EPA notes that reducing levels below 2 pCi/L is difficult. Still, test again in the future, especially after renovations or changes in how you use the home.

EPA stresses that there is no known safe level of radon. Lower is better.

How U.S. levels compare internationally

The World Health Organization recommends a national reference level of 100 Bq/m³ (about 2.7 pCi/L) to minimize health hazards from indoor radon, and says that where this can't be done, the level shouldn't exceed 300 Bq/m³ (about 8.1 pCi/L). Other countries set their own levels. Some are lower than EPA's 4 pCi/L and some higher. If you're reading foreign guidance, convert units before comparing.

Translating results into risk

EPA's risk tables estimate how many people out of 1,000 could get lung cancer from a lifetime of exposure:

Level	Never smoked	Smokers
4 pCi/L	about 7	about 62
2 pCi/L	about 4	about 32
1.3 pCi/L	about 2	about 20

These are population estimates, not a personal prediction, but they show why EPA recommends action at 4 pCi/L and suggests considering it from 2 pCi/L.

If you have two results that disagree

It's normal for results to vary. Radon changes with weather, season, ventilation, and HVAC operation. EPA's follow-up approach:

• First short-term test at or above 4 pCi/L: do a second test.
• If the follow-up is a long-term test: fix the home if the long-term result is 4 pCi/L or more.
• If the follow-up is a second short-term test: fix the home if the average of the two is 4 pCi/L or more.

If one result is far higher than the other, check whether conditions differed. Were windows opened, was the kit moved, or did it sit in the mail? Consider a long-term test for the clearest picture.

Results from digital monitors

Consumer digital monitors show running averages and day-to-day swings. Look at the long-term average (30 days or more) rather than daily spikes. For decisions about mitigation or real estate, confirm with a lab-analyzed test or a professional measurement.

Next steps by level

4 pCi/L or higher (confirmed):

1. Get estimates from qualified mitigation contractors. Your state radon office can help you find them.
2. Ask about the system design, fan location, discharge above the roof, warning device, and post-mitigation guarantee.
3. After installation, test within 30 days but no sooner than 24 hours after the system starts.

2 to 4 pCi/L:

1. Consider a long-term test to learn your year-round average.
2. Weigh mitigation, especially if anyone in the home smokes or spends a lot of time on the lowest level.

Below 2 pCi/L:

1. Keep your report.
2. Retest after renovations, when you start using a lower level, or every few years.

Common reasons a result might be unreliable

• Windows or doors were left open during a short-term test.
• The device was placed in the wrong spot: on the floor, in a closet, next to a sump, in a bathroom, or near a heat source or draft.
• The kit was mailed late. Many short-term kits must reach the lab within a few days of the end of the test.
• Dates or times weren't recorded, so the lab can't calculate an accurate result.
• The test was disturbed: moved, covered, or handled during the test.
• Unusual weather, such as a major storm, affected a very short test.

If any of these happened, retest rather than relying on the number.

Keep your records

Save every report, including dates, locations, and device types. They're useful for future comparisons, for real estate transactions, and for confirming that a mitigation system is working over time.

Key takeaways

• 1 pCi/L equals 37 Bq/m³, so 4 pCi/L is about 150 Bq/m³.
• EPA says to fix at 4 pCi/L or higher and to consider fixing between 2 and 4.
• The average U.S. indoor level is about 1.3 pCi/L, and outdoor air averages about 0.4.
• Confirm high results with a follow-up test before deciding.
• Check the report for dates, placement, and validity notes.