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Radon Levels

Radon level of 12 pCi/L: what it means and what to do

By Radon411 Editorial Team

Updated October 1, 2026

Methodology

Try it

Move a reading around 12 pCi/L

The reading starts at 12 pCi/L. Slide it to see where EPA's guidance changes and how far this number is from each line.

Read a result for 12 pCi/L

Starts at 12.0 pCi/L, this page's reading

12.0pCi/L

EPA’s own thresholds, as its guidance states them.

EPA’s reading of 12.0 pCi/L

At or above 4 pCi/L

  1. Under 20 to 1.9 pCi/L
  2. 2 to 4consider a fix
  3. 4 and aboveEPA says fix it

This result is at or above 4 pCi/L. EPA recommends fixing a home when the radon level is 4 pCi/L or higher. That is 8.0 pCi/L above EPA's action level, 3.0 times it.

Interpret this readingWhat a fix costs

Short answer

A radon level of 12 pCi/L is high: it is three times the action level, and EPA recommends fixing the home once a second test confirms it. Because it is more than twice the action level, a first short-term result this high calls for a second short-term test immediately.

Next step: pick the right test for your home. Which test to use

Key takeaways

  • 12 pCi/L is 3 times EPA's 4 pCi/L action level.
  • More than twice the action level: confirm right away, then fix.
  • EPA estimates the average U.S. home at about 1.3 pCi/L; 12 pCi/L is 9.23 times that.
  • Confirm a first short-term result this high with a second short-term test immediately.

Where it sits

Is a radon level of 12 pCi/L high?

On the risk chart, 12 falls between the 10 pCi/L row (about 150 lung cancers per 1,000 people who smoked, about 18 per 1,000 who never smoked) and the 20 pCi/L row (about 260 and about 36), over a lifetime of exposure. Readings such as 11 or 12.5 sit in the same place.

About 445 Bq/m3
12 pCi/L in becquerels per cubic meter, at about 37 Bq/m3 per pCi/L (calculated).
3 times
EPA's 4 pCi/L action level (calculated).
9.23 times
The U.S. indoor average of about 1.3 pCi/L (calculated).
Read moreThree paragraphs and a table, 1 min

The fix is the same work as at lower readings. The number and location of suction pipes a system needs depends on how easily air can move under the slab and on the strength of the radon source, and a contractor may run diagnostic tests first to design it.

At about 444 , 12 pCi/L is 30 times the outdoor average and about nine times EPA's estimate of the average indoor level, by our calculation. A reduction of about 83% would bring it to 2 pCi/L; EPA puts some radon reduction systems at up to 99 percent, so a reading of 12 is fixable to the level most homes reach.

Where 12 pCi/L sits against EPA's and WHO's reference points

  • Against outdoor air (about 0.4 pCi/L)

    30 times the outdoor average (calculated)

  • Against WHO's recommended reference level (100 Bq/m3, 2.7 pCi/L)

    Above it

  • EPA's band

    More than twice the action level: confirm right away, then fix

Other readings explained: 1 pCi/L, 2 pCi/L, 3 pCi/L, 4 pCi/L, 5 pCi/L, 6 pCi/L, 7 pCi/L, 8 pCi/L, 10 pCi/L, 20 pCi/L, 30 pCi/L, 100 pCi/L.

What to do

What to do about a radon level of 12 pCi/L

EPA recommends fixing a home when the radon level is 4 pCi/L or higher. For a reading of 12 pCi/L, the steps come to this:

Steps for a reading of 12 pCi/L

  1. Retest right away

    12 pCi/L is 3 times the action level, more than twice it, so take a second short-term test immediately rather than wait for a long-term test.

  2. Check the first test

    Improper testing may give inaccurate results; confirm the device, its placement and closed-house conditions.

  3. Fix the home

    EPA recommends fixing a home when the radon level is 4 pCi/L or higher. Get estimates from qualified contractors; see radon mitigation.

  4. Test after the fix

    No sooner than 24 hours and within 30 days after the system starts, then at least every two years.
Read moreA paragraph, 1 min

The full sequence of tests, from a first result to the decision to fix, is drawn on radon testing.

Health risk

The lung cancer risk at 12 pCi/L

EPA's risk chart has no row for 12 pCi/L, so the table shows the rows either side of it. The chart estimates how many people out of 1,000 could get lung cancer if exposed to a level over a lifetime, for people who smoked and people who never smoked.

EPA's risk chart rows around 12 pCi/L
Radon levelPeople who smokedPeople who never smokedWhat to do
20 pCi/L (740 Bq/m3)About 260 in 1,000About 36 in 1,000Fix your home
10 pCi/L (370 Bq/m3)About 150 in 1,000About 18 in 1,000Fix your home
Read moreTwo paragraphs, 1 min

12 pCi/L sits between the 10 and 20 pCi/L rows, a quarter of the way from the lower row (our calculation). At 20 pCi/L the chart gives about 260 in 1,000 people who smoked (250 times the risk of drowning), and about 36 in 1,000 who never smoked (35 times the risk of drowning); at 10 pCi/L, about 150 in 1,000 people who smoked (200 times the risk of dying in a home fire), and about 18 in 1,000 who never smoked (20 times the risk of dying in a home fire).

Lung cancer risk is estimated to rise by about 16% per 100 Bq/m3 of long-term average radon. At 445 Bq/m3, a long-term average of 12 pCi/L, that comes to about 71% above the risk with no radon at all (our calculation, a population estimate, not a forecast for one person); a former smoker's risk may sit between the chart's two columns.

How sure

How certain is a reading of 12 pCi/L?

At 12 pCi/L the question is not whether the home is high but how high, since a day-to-day or seasonal swing cannot explain a reading this far above the : even if this result ran twice the year-round average, the home would still sit at 6 pCi/L, at or above the action level.

Read moreA note, 1 min

With a system

How much a radon system would lower 12 pCi/L

From 12 pCi/L, an active system at the low end of its typical range would leave about 6 pCi/L, still at or above the action level, so the test after installation decides whether the system is enough; at the high end, about 0.12 pCi/L. Our arithmetic on the published ranges, not a prediction for your house: radon levels in most homes can be reduced to 2 pCi/L or below.

What the typical reductions would leave from 12 pCi/L (calculated)
TechniqueTypical reductionFrom 12 pCi/L, about
Active suction: sub-slab, sump hole, drain tile, or a crawl-space membrane50 to 99 percent6 to 0.12 pCi/L
Passive sub-slab suction (no fan)30 to 70 percent8.4 to 3.6 pCi/L
Read moreA paragraph, 1 min

Which technique fits depends on the foundation; see radon mitigation systems, and for cost, radon mitigation cost.

Situations

Where people meet a reading of 12 pCi/L

12 pCi/L in three common situations

  • 12 pCi/L on a first short-term test

    Take a second short-term test immediately. EPA recommends fixing the home when the average of the two short-term tests is 4 pCi/L or more, which a first result of 12 makes very likely.

  • Designing a system for 12 pCi/L

    How many suction pipes a system needs, and where, depends on how easily air moves under the slab and on the strength of the radon source. The contractor may run diagnostic tests during the first phase of the installation.

  • 12 pCi/L in a home sale

    The buyer and seller should discuss the timing and costs of radon reduction, and write into the contract when mitigation will be done and who will pay for it.

Retest

When to retest after 12 pCi/L

12 pCi/L is three times the action level, so the rule for a first result more than twice 4 pCi/L applies: take a second immediately, not a long-term one. Once a system is running, a two- to seven-day test within 30 days shows how far the level came down, and a retest at least every two years shows it has stayed there.

When to test again after a reading of 12 pCi/L
WhenWhat to do
To confirm the first resultImmediately, with a second short-term test
After a system is installedNo sooner than 24 hours and within 30 days, with a two- to seven-day test
With a system in placeAt least every two years
After a remodelIn the lowest lived-in area
Show all 4 rows
Read moreA paragraph, 1 min

The general answer is on how often should I test for radon.

Questions

Radon level of 12 pCi/L: questions

Is 12 pCi/L of radon safe?

No. 12 pCi/L is at or above EPA's 4 pCi/L action level, where EPA recommends fixing the home once the result is confirmed.

Do I need radon mitigation at 12 pCi/L?

Yes, by EPA's guidance, once a long-term test or the average of two short-term tests confirms the level is 4 pCi/L or more; 12 pCi/L is 3 times that line.

What is 12 pCi/L in Bq/m3?

It is about 445 Bq/m3, at about 37 Bq/m3 per pCi/L (our calculation).

Should I buy a house with a radon level of 12 pCi/L?

A high level is fixable: from 12 pCi/L, an active system's typical reduction would leave 6 pCi/L or less. Buyers and sellers should discuss the timing and costs of radon reduction, and the contract can say when mitigation happens and who pays. See should I buy a house with radon.

Is 12 pCi/L in a basement different from upstairs?

Usually the basement reads higher. If 12 pCi/L came from a room upstairs, a basement half again as high would read 18 pCi/L, at or above the action level; a test belongs in the lowest lived-in level.

How long should I wait to retest after 12 pCi/L?

Do not wait: 12 pCi/L is more than twice the action level, and a first short-term result that high calls for a second short-term test immediately.

How far would a system bring 12 pCi/L down?

Active soil suction typically cuts radon by 50 to 99 percent: from 12 pCi/L, to 6 pCi/L or lower at the low end (our calculation). Reaching 2 pCi/L takes a cut of about 83 percent, inside that range. The post-mitigation test shows the real result.

Is 12 pCi/L above the WHO limit?

Yes. WHO says national reference levels should not exceed 8.1 pCi/L (300 Bq/m3), and 12 pCi/L is about 444 Bq/m3 (our calculation), about one and a half times that.