A note before you read. This article is general health and reference information drawn from publicly available Health Canada, World Health Organization, US Environmental Protection Agency, and Canadian Cancer Society publications. It is not medical advice. See full disclaimers at the bottom.
Quick answer. In Canada, the radon action level is 200 Bq/m³ (Health Canada residential guideline). The World Health Organization recommends 100 Bq/m³. The US EPA action level is 4 pCi/L (148 Bq/m³). Conversion: 1 pCi/L = 37 Bq/m³. For Canadian homes, every regulator (BCFSA, RECA, OACIQ, NBREA), every provincial real-estate framework, and the Tarion new-home warranty in Ontario all reference 200 Bq/m³. Use 200 Bq/m³ as your action threshold; treat WHO's 100 Bq/m³ as a longer-term aspirational target if you want to drive risk lower.
If you've spent any time researching radon, you've probably encountered three different action-level numbers and wondered which one to use:
- Health Canada: 200 Bq/m³ (becquerels per cubic metre) — the Canadian residential action guideline
- World Health Organization (WHO): 100 Bq/m³ — the WHO's recommended reference level
- United States EPA: 4 pCi/L (≈ 148 Bq/m³) — the US action level
Three different authorities. Three different numbers. The differences are not arbitrary — they reflect different national risk-benefit calculations, different baseline radon profiles, and different policy histories. But for a Canadian homeowner trying to decide what to do about a test result, the question is simple: which one applies to me?
Short answer: In Canada, you compare your radon test result to the Health Canada guideline of 200 Bq/m³. That's the published Canadian standard, the threshold above which Health Canada recommends mitigation, the number every Canadian regulator (Tarion, BCFSA, RECA, OACIQ) operates around, and the figure your real estate lawyer will use. The WHO 100 Bq/m³ figure is informative context (and some Canadians choose to mitigate at lower levels because of it), and the US EPA 148 Bq/m³ figure becomes relevant if you're reading American radon content or buying property in the US — but it doesn't apply to Canadian homes.
This guide explains what each number means, why they're different, how to convert between Bq/m³ and pCi/L, and what each guideline would say about your specific test result.
TL;DR
- Canadian homeowners use the Health Canada 200 Bq/m³ guideline. That's the published Canadian standard.
- WHO 100 Bq/m³ is a more conservative reference level that some Canadians choose to act on voluntarily (the Canadian Cancer Society notes that no level of radon exposure is considered free of risk).
- US EPA 148 Bq/m³ (= 4 pCi/L) applies to homes in the United States. It's the most common American reference because the US uses pCi/L (picocuries per litre), not Bq/m³.
- Conversion: 1 pCi/L ≈ 37 Bq/m³. So 4 pCi/L ≈ 148 Bq/m³.
- The only way to know your home's level is to test it. Order a $89 long-term radon test kit →
Table of contents
- Quick answer: which guideline applies to you
- The three guidelines explained
- Why the three numbers are different
- Bq/m³ vs pCi/L — how to convert
- Decision matrix: what each guideline would say about your result
- The "as low as reasonably achievable" principle
- FAQ
- Disclaimers
- Sources
Quick answer: which guideline applies to you
If you live in Canada and you're testing your Canadian home: use the Health Canada 200 Bq/m³ guideline. That's the published Canadian standard. Above 200 Bq/m³, Health Canada recommends taking corrective action (Health Canada — Testing your home for radon). Tarion's Ontario new-home warranty triggers at the same 200 Bq/m³ figure. BCFSA, RECA, and OACIQ real estate disclosure rules all reference 200 Bq/m³ as the "material latent defect" threshold.
If you want a more conservative personal threshold: use the WHO 100 Bq/m³ reference level. The Canadian Cancer Society notes that no level of radon exposure is considered free of risk and recommends reducing to as low as reasonably achievable. Some Canadian homeowners voluntarily act below 200 Bq/m³ — particularly families with children, smokers/former smokers, or people who spend a lot of time in their basement.
If you're reading American radon content (EPA, US cancer society, US contractors): the US EPA 148 Bq/m³ (= 4 pCi/L) action level is what they're referencing. It's not the Canadian standard, and Canadian regulators don't use it.
If you own property both in Canada and the US: each property follows its own country's standard. A 4 pCi/L US action level (148 Bq/m³) would not trigger the Canadian Health Canada guideline (200 Bq/m³), but a 200 Bq/m³ Canadian result would absolutely exceed the US EPA threshold. The US guideline is the more conservative of the two.
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The three guidelines explained
Health Canada — 200 Bq/m³ (Canada)
Canada's national residential radon guideline is 200 Bq/m³, established by Health Canada in 2007 (replacing an earlier 800 Bq/m³ guideline that had been in place since 1988). The guideline applies to "normal occupancy areas" of homes — typically the lowest lived-in level (basements where habitable, otherwise main floor).
Per Health Canada's published guidance (Guide for Radon Measurements in Residential Dwellings):
- Above 200 Bq/m³: corrective action recommended, ideally within 1 year (sooner if levels are much higher).
- At or below 200 Bq/m³: no corrective action required. Health Canada recommends retesting every 5 years.
The 200 Bq/m³ guideline is the legal and regulatory reference point in Canada. Tarion's Ontario new-home warranty triggers at this level. BCFSA, RECA, and OACIQ all reference 200 Bq/m³ for real estate disclosure obligations. Every Canadian municipal radon program (Hamilton, Guelph, Kingston) is built around the same number.
World Health Organization — 100 Bq/m³ (international reference)
The WHO published a Handbook on Indoor Radon in 2009 that recommended a national reference level of 100 Bq/m³ wherever achievable, with an upper limit of 300 Bq/m³ where 100 Bq/m³ is not feasible. The WHO's stated rationale is that lung cancer risk associated with radon increases continuously below the 200 Bq/m³ Canadian level and below the 4 pCi/L US level — no level of radon exposure is considered free of risk, and lower exposure is associated with lower risk in absolute terms.
The WHO's 100 Bq/m³ recommendation is not legally binding anywhere. It's a reference standard that individual countries consider when setting their own guidelines. Canada's Health Canada and the Canadian Cancer Society both reference the WHO recommendation and acknowledge that lower-than-200 Bq/m³ readings still carry some long-term lung cancer risk.
US Environmental Protection Agency — 4 pCi/L (148 Bq/m³) (United States)
The US EPA's residential radon action level is 4 pCi/L, established in 1986. In SI units, 4 pCi/L = approximately 148 Bq/m³. The EPA recommends:
- At or above 4 pCi/L (148 Bq/m³): take action to reduce radon levels.
- Between 2 and 4 pCi/L (74–148 Bq/m³): consider taking action.
- Below 2 pCi/L (74 Bq/m³): no action recommended, though lower exposure is associated with lower long-term risk.
The US EPA action level is more conservative than the Canadian guideline — 4 pCi/L (148 Bq/m³) is below Canada's 200 Bq/m³. The US uses different units (pCi/L) than the rest of the world (Bq/m³), which is the source of much of the confusion when Canadian readers encounter American radon content.
Why the three numbers are different
The differences aren't arbitrary — they reflect three different things:
1. Different cost-benefit calculations. Each authority weighs the cost of mitigating large numbers of homes against the public-health benefit of the resulting reduction in lung cancer cases. Lower thresholds mean more homes flagged, more mitigation cost, and more lung cancer cases prevented at the population level. Higher thresholds mean fewer homes affected, lower aggregate mitigation cost, but more cancer cases not prevented. Each authority lands in a different place on this trade-off.
2. Different baseline radon profiles. The US has a population-weighted average residential radon level different from Canada's, and from European countries the WHO references. A guideline level that flags 7% of Canadian homes might flag a substantially different proportion of American or European homes — affecting the cost-benefit math.
3. Different policy histories. The EPA's 4 pCi/L action level has been in place since 1986 and is deeply embedded in American real estate practice, building codes, mitigation standards, and consumer awareness. Health Canada's 200 Bq/m³ guideline replaced an older 800 Bq/m³ standard in 2007. The WHO's 100 Bq/m³ recommendation came in 2009. Each guideline's history shapes its position.
What's NOT the difference: the underlying lung-cancer risk per unit of radon exposure is the same in all three jurisdictions. Radon causes lung cancer the same way in Calgary, Denver, and Berlin. The science is the same; the policy thresholds are different.
Bq/m³ vs pCi/L — how to convert
This is the part that confuses everyone reading across the Canada-US border.
Becquerels per cubic metre (Bq/m³): the SI (metric) unit used in Canada, the WHO, and most of the world. One becquerel = one radioactive decay event per second. A radon level of 200 Bq/m³ means 200 decay events per second per cubic metre of air.
Picocuries per litre (pCi/L): the imperial unit used by the US EPA and US contractors. One picocurie ≈ 0.037 becquerels.
Conversion factor:
- 1 pCi/L = 37 Bq/m³
- 1 Bq/m³ = 0.027 pCi/L
Common conversion table
| pCi/L (US) | Bq/m³ (Canada / WHO) | What it means |
|---|---|---|
| 1 pCi/L | ~37 Bq/m³ | Below all guidelines; below average Canadian indoor radon |
| 2 pCi/L | ~74 Bq/m³ | Below all guidelines; "consider action" zone in US EPA framing |
| 2.7 pCi/L | ~100 Bq/m³ | At the WHO recommended reference level |
| 4 pCi/L | ~148 Bq/m³ | At the US EPA action level; below Health Canada guideline |
| 5.4 pCi/L | ~200 Bq/m³ | At the Health Canada residential guideline |
| 8 pCi/L | ~296 Bq/m³ | Above all three guidelines |
| 10 pCi/L | ~370 Bq/m³ | Well above all guidelines |
| 20 pCi/L | ~740 Bq/m³ | Significantly elevated |
Practical tip for Canadians reading US content: when you see a "4 pCi/L" reference in American radon coverage, mentally translate to "about 148 Bq/m³" — that's the US action level, below the Canadian Health Canada guideline. When you see "2 pCi/L," that's about 74 Bq/m³ — well below all three guidelines.
Decision matrix: what each guideline would say about your result
Here's how each authority would interpret a Canadian home's long-term radon test result:
| Your result | Health Canada (200 Bq/m³) | WHO (100 Bq/m³) | US EPA (148 Bq/m³ / 4 pCi/L) |
|---|---|---|---|
| < 50 Bq/m³ (≈ < 1.4 pCi/L) | No action; below average Canadian level | No action | No action |
| 50–100 Bq/m³ (≈ 1.4–2.7 pCi/L) | No action | At/approaching WHO reference | "Consider action" zone |
| 100–148 Bq/m³ (≈ 2.7–4 pCi/L) | No action | Above WHO reference | Below US action level |
| 148–200 Bq/m³ (≈ 4–5.4 pCi/L) | No action | Above WHO reference | Above US action level |
| 200–400 Bq/m³ (≈ 5.4–11 pCi/L) | Action recommended | Above WHO reference | Above US action level |
| > 400 Bq/m³ (≈ > 11 pCi/L) | Action recommended (sooner if much higher) | Above WHO reference | Above US action level |
For a Canadian home, the Health Canada column is the binding one. The WHO and US EPA columns are reference context — useful for understanding international perspectives, but not the standard your Canadian regulator, lawyer, or warranty provider will use.
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The "as low as reasonably achievable" principle
The Canadian Cancer Society's published guidance includes this important framing:
The Canadian Cancer Society's published position is that no level of radon exposure is considered free of risk, and that levels should be reduced to as low as reasonably achievable. (Canadian Cancer Society — Radon)
This "as low as reasonably achievable" (ALARA) principle is shared across radiation-protection science generally. It explains why the WHO recommends 100 Bq/m³, why the US EPA uses a more conservative 148 Bq/m³, and why some Canadians voluntarily act on radon levels below the Health Canada 200 Bq/m³ guideline:
- Lung cancer risk associated with radon is a continuum. Risk does not jump abruptly at any threshold. A 150 Bq/m³ home has lower risk than a 200 Bq/m³ home; a 100 Bq/m³ home has lower risk than a 150 Bq/m³ home; and so on.
- Mitigation is generally feasible at any reading where it's worth the cost. Sub-slab depressurization can typically reduce indoor radon by up to 95% regardless of the starting level.
- Some Canadians choose to mitigate below 200 Bq/m³ for personal-risk reasons — typically families with children, smokers and former smokers, or people who spend significant time in their basement.
There's no wrong answer here for a Canadian homeowner with a result between 100 and 200 Bq/m³. No action is required by the Canadian guideline, but acting voluntarily is consistent with the ALARA principle and with WHO guidance. This is a personal decision based on the specific home, the people living in it, and the cost-benefit math for that household.
FAQ
Which radon level should I use as my action threshold in Canada? 200 Bq/m³ — the Health Canada residential guideline. That's the published Canadian standard, the figure Tarion (Ontario new-home warranty) triggers at, and the threshold all Canadian regulators (BCFSA, RECA, OACIQ) reference for real estate disclosure.
Why is the WHO's 100 Bq/m³ recommendation different from Canada's 200 Bq/m³? The WHO recommends 100 Bq/m³ as a reference level wherever achievable, based on the principle that lung cancer risk from radon is a continuum and lower exposure is associated with lower risk in absolute terms. The WHO recommendation isn't legally binding anywhere — individual countries set their own guidelines based on national cost-benefit calculations. Canada has chosen 200 Bq/m³ as the action threshold.
Is the US EPA's 4 pCi/L the same as Canada's 200 Bq/m³? No. 4 pCi/L = approximately 148 Bq/m³, which is below Canada's 200 Bq/m³ Health Canada guideline. The US EPA's action level is more conservative than the Canadian standard.
How do I convert between pCi/L and Bq/m³? 1 pCi/L = 37 Bq/m³. So multiply pCi/L by 37 to get Bq/m³, or multiply Bq/m³ by 0.027 to get pCi/L. See the conversion table above.
My radon test came back at 150 Bq/m³. What should I do? Per Health Canada, no action is required (you're below the 200 Bq/m³ guideline). But you're above the WHO 100 Bq/m³ reference level and above the US EPA 148 Bq/m³ action level. Some Canadians in this range choose to mitigate voluntarily — particularly families with children, smokers/former smokers, or people who spend a lot of time in their basement. The Canadian Cancer Society notes that no level of radon exposure is considered free of risk, and recommends reducing levels to as low as reasonably achievable. This is a personal decision based on your household.
My radon test came back at 4 pCi/L. What should I do? Convert first: 4 pCi/L = ~148 Bq/m³. That's at the US EPA action level (you'd mitigate in the US) but below Canada's Health Canada guideline (no required action in Canada). See the decision matrix above.
Why does Canada use a higher threshold than the US? Different national risk-benefit calculations. Canada's 200 Bq/m³ guideline reflects a balance between population-wide mitigation cost and lung-cancer-prevention benefit specific to the Canadian residential housing stock and indoor radon profile. The US EPA's 4 pCi/L (148 Bq/m³) action level reflects a similar balance with different inputs. Neither number is "right" or "wrong" — they're policy thresholds reflecting different national contexts.
Are there any Canadian provinces using a stricter guideline than 200 Bq/m³? For residential homes, no — all Canadian provinces use the Health Canada 200 Bq/m³ guideline. Saskatchewan does set a more stringent 112 Bq/m³ action level for schools (recognizing that children spend long durations in school buildings over many years), but this applies to public school buildings, not private residences.
Is a reading below 100 Bq/m³ free of risk? The Canadian Cancer Society's published position is that no level of radon exposure is considered free of risk — any radon exposure carries some long-term lung cancer risk. The 100 Bq/m³ WHO reference and 200 Bq/m³ Canadian guideline are policy thresholds, not absolute risk boundaries. Lower exposure is always associated with lower risk.
What's the radon level outdoors? Outdoor radon levels are typically very low — between 5 and 15 Bq/m³ in most locations, due to atmospheric dilution. The radon concern is indoors, where the gas can accumulate in enclosed spaces with limited fresh air exchange.
Test your home — the only way to know which guideline applies to you
Whichever guideline you choose to act on — Health Canada 200, WHO 100, US EPA 148 — you first need to know your home's actual level. The only way to know is to test.
RadonTest.ca — $89 all-in (plus applicable tax). Long-term 91-day alpha-track test kit. C-NRPP-listed device. Analysed at Lex Scientific in Guelph, Ontario — Canadian lab, C-NRPP listed, ISO/IEC 17025 accredited by CALA. Tracked Canadian shipping both ways. Written lab report PDF delivered to your inbox in Bq/m³ (the Canadian unit) — easy to compare to any of the three international guidelines.
Important disclaimers
Not medical advice. This article provides general health and reference information drawn from publicly available Health Canada, World Health Organization, US Environmental Protection Agency, and Canadian Cancer Society materials. It is not medical advice and is not a substitute for advice from a qualified medical professional. If you have any health concerns, please consult a physician.
Statistics and citations. Health Canada figures are taken from Health Canada — Testing your home for radon and the Guide for Radon Measurements in Residential Dwellings. WHO figures are from the WHO Handbook on Indoor Radon (2009) and subsequent WHO publications. US EPA figures are from the US EPA's residential radon program. Canadian Cancer Society quotation is from cancer.ca. Sources update published figures periodically; figures cited reflect the sources as of May 2026.
Conversion. The 1 pCi/L = 37 Bq/m³ conversion factor is a rounding of the more precise figure (1 pCi/L = 37.0 Bq/m³). Differences in significant figures may produce small variations in published conversion tables. The conversion is a physical constant, not a policy choice.
Personal action below 200 Bq/m³. Statements about Canadians voluntarily acting on radon levels below the Health Canada 200 Bq/m³ guideline reflect general public-health communication and the Canadian Cancer Society's "as low as reasonably achievable" framing. Whether to mitigate at lower levels is a personal household decision based on individual circumstances. This article does not recommend any specific action for any specific reader; consult a qualified C-NRPP-certified professional for personalized guidance.
Legal and regulatory references. Statements about Canadian regulatory standards (Tarion, BCFSA, RECA, OACIQ, NBREA, municipal programs) reflect publicly available authority guidance. Specific obligations for any individual transaction or claim depend on the facts; consult a qualified professional in your province.
No diagnosis or treatment claims. RadonTest.ca sells radon test kits. We do not diagnose, treat, or prevent disease.
No warranty as to completeness. RadonTest.ca makes no warranty as to the completeness or accuracy of the information herein and accepts no liability for decisions made in reliance on this article.
Sources & further reading
Health Canada
- Radon — What You Need to Know (Health Canada, 2025)
- Testing your home for radon
- Guide for Radon Measurements in Residential Dwellings
- Radon Reduction Guide for Canadians
World Health Organization
US Environmental Protection Agency
Canadian Cancer Society and research
- Canadian Cancer Society — Radon
- International Agency for Research on Cancer (IARC) — IARC classifies radon as a Group 1 carcinogen
Canadian associations
- C-NRPP — Find a Certified Professional / Lab
- CARST — Canadian Association of Radon Scientists and Technologists
- Take Action on Radon
Related RadonTest.ca articles
- Symptoms of Radon Exposure: What Canadians Should Know
- Best Radon Test Kit in Canada (2026)
- Long-Term Radon Test vs Continuous Digital Monitor
- Radon Testing When Buying or Selling a Home in Canada
- Canadian Building Codes and Radon: 2026 Guide
- How to Read Your Radon Test Results
- What to Do If Your Radon Level Is Above 200 Bq/m³