Radon unit converter: pCi/L, Bq/m³ and working levels

Radon results come in whatever unit the lab or the monitor's maker prefers. A mail-in kit from a U.S. lab reports picocuries per liter. A monitor designed for European or Canadian homes may show becquerels per cubic meter. Older mine and workplace records, and a few professional instruments, use working levels. This gauge puts any of the three on one scale and lines it up against the reference levels that agencies in the U.S., Canada, Europe and the World Health Organization have published.

Type the number from your report or screen into Radon reading, then pick the matching option under Unit on your report or monitor: pCi/L (picocuries per liter), Bq/m³ (becquerels per cubic meter) or WL (working level). The answer updates as you type. It is for radon in indoor air; a radon-in-water result belongs to a different kind of test, covered in the questions below.

How it works

The conversion between the two common units is fixed. One picocurie is 0.037 becquerel, and a cubic meter holds 1,000 liters, so 1 pCi/L equals 37 Bq/m³. Working levels are a different kind of measurement: they count the energy of radon's short-lived decay products, not the gas itself. To bridge them the gauge follows the EPA's convention, which assumes the decay products sit at 50% equilibrium with the gas. On that assumption, 1 WL is about 200 pCi/L.

Bq/m³ = pCi/L × 37, and WL = pCi/L ÷ 200

The readout, titled "Your reading on one scale", shows your reading in pCi/L as the big figure. Under it runs a banded scale from 0 to 8 pCi/L with three bands, all drawn from EPA guidance because pCi/L is the U.S. unit: below the EPA's 2 pCi/L "consider fixing" point, from 2 up to 4 pCi/L where the EPA suggests considering a fix, and at or above the EPA's 4 pCi/L action level. Then come your reading in Bq/m³ and in working levels, and five reference lines, each converted to pCi/L so you can compare like with like.

Worked example

The gauge opens on 4 pCi/L, the EPA's action level. The marker sits exactly halfway along the 0 to 8 scale, on the EPA's 4 pCi/L line, and the band reads "At or above the EPA's 4 pCi/L action level". The readout shows:

• In Bq/m³: 148
• In working levels (EPA 50% equilibrium): 0.02
• US EPA: consider fixing (2 pCi/L): 2 pCi/L
• WHO reference level (100 Bq/m³): 2.7 pCi/L
• US EPA action level (4 pCi/L): 4 pCi/L
• Health Canada guideline (200 Bq/m³): 5.41 pCi/L
• EU upper reference level (300 Bq/m³): 8.11 pCi/L

The same air reads very differently depending on whose yardstick you hold up. At 148 Bq/m³ it is above the WHO's 100, below Health Canada's 200 and below the EU's 300, and right on the EPA's action level. Work it backward and a Canadian report of 200 Bq/m³ comes to about 5.41 pCi/L, which is over the EPA's 4.

Whose numbers these are

Each reference line is one agency's own figure, set for its own country or audience and revised from time to time, so check the current version at the source before you act on one.

The U.S. EPA's action level is 4 pCi/L, and it suggests considering a fix between 2 and 4. The WHO's reference level is 100 Bq/m³, about 2.7 pCi/L. Health Canada's guideline is 200 Bq/m³, about 5.4. Under the EU's 2013 directive, member states set national reference levels no higher than 300 Bq/m³, about 8.1.

None of these is a line between safe and unsafe. Risk rises with concentration and with years of exposure, and the EPA's guidance is that any radon exposure carries some risk. The gauge converts units. It does not judge a house, and it cannot tell you whether one reading reflects your yearly average. Asking whose scale a number sits on helps with outdoor air too, as our explainer on the Air Quality Index shows.

That depends on the test. Short-term tests run 2 to 90 days and long-term tests more than 90. Short-term tests need closed-house conditions: windows and outside doors shut except for normal coming and going, starting 12 hours before the test. Place the detector on the lowest lived-in level, away from drafts, sump pits and exterior walls. A single short-term result is a reason to test again, not a verdict, and our longer piece on radon at home walks through the follow-up sequence and how a fix works. When a fix is needed, it is usually sub-slab depressurization: a pipe through the floor and a fan that draws soil gas out from under the house.

One more caution about working levels. Real homes do not sit at exactly 50% equilibrium; dust, air movement and ventilation shift the balance. Treat any conversion between working levels and pCi/L as approximate, and ask whoever took a WL reading how to interpret it.

Sources

• The U.S. EPA's A Citizen's Guide to Radon, for the 4 pCi/L action level, the 2 to 4 pCi/L range and the testing sequence, with current guidance on the EPA's radon pages.
• The World Health Organization's handbook on indoor radon, for the 100 Bq/m³ reference level.
• Health Canada's radon guideline of 200 Bq/m³.
• The EU's 2013 basic safety standards directive (Council Directive 2013/59/Euratom), for the 300 Bq/m³ upper reference level.
• Unit definitions: 1 pCi = 0.037 Bq, and the EPA's 50% equilibrium convention for working levels.

Questions

Why does my monitor show Bq/m³ when my lab report says pCi/L?

Monitors built for markets outside the U.S. often default to becquerels, and some let you switch units in their settings. Multiply pCi/L by 37 to get Bq/m³, or divide Bq/m³ by 37 to go the other way. The gauge does it both ways.

Is 148 Bq/m³ high?

It depends on whose figure you use. It equals the EPA's 4 pCi/L action level, sits above the WHO's 100 Bq/m³ reference level and below Health Canada's 200. The gauge shows where your number falls against each agency's line; the decision about your house rests on a proper test and the guidance where you live.

Can I enter a radon-in-water result here?

No. Radon in well water is also reported in pCi/L, but per liter of water, and it is a different measurement from radon in air. A common rule of thumb is that 10,000 pCi/L in water adds about 1 pCi/L to indoor air. There is no enforceable federal limit for private wells, and treatment is aeration or granular activated carbon. If you are on a well, our well shock chlorination calculator covers the other routine job: disinfecting it.

How exact is the working-level conversion?

Only as exact as its assumption. The gauge uses the EPA's 50% equilibrium convention, so 1 WL counts as about 200 pCi/L. A house at a different equilibrium would give a different conversion, so read the result as an estimate.