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Radon Levels by Country

Radon Levels by Country: How Safety Thresholds Differ Around the World
Radon Levels by Country: How Safety Thresholds Differ Around the World

Radon Levels by Country: How Safety Thresholds Differ Around the World

“What radon level is dangerous?” sounds like it should have one clean answer. In reality, different countries use different numbers, different units, and even different terms. Some call it an action level. Others call it a reference level or guideline. The numeric thresholds vary widely, but the goal is usually the same: set a practical trigger where governments recommend (or require) testing, mitigation, and building controls.

This pillar guide explains how radon thresholds differ around the world, why those differences exist, and how to interpret them as a homeowner, renter, builder, or buyer. We will also include a country-by-country reference table (with sources) so you can quickly see how your country compares.

Important reality check: There is no known safe level of radon exposure. Risk generally rises as radon increases. Many national thresholds are policy triggers, not magic “safe lines.” The CDC explicitly notes there is no known safe level of radon and recommends action at and even below the EPA level. CDC: Testing for Radon in Your Home

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Radon basics and why countries set different numbers

Radon is a naturally occurring radioactive gas that comes from uranium in soil and rock. Outdoors it usually dilutes quickly. Indoors it can accumulate, especially in lower levels of a building and in homes with limited ventilation. The World Health Organization notes that indoor radon can vary substantially, ranging from around 10 Bq/m³ to more than 10,000 Bq/m³ depending on the building and conditions. WHO: Radon and health

The health concern is primarily lung cancer. WHO estimates radon contributes a meaningful share of lung cancers, and the share varies by country based on national radon levels and smoking prevalence. WHO: Radon and health Smoking matters because radon risk and smoking risk interact. In a country with heavy smoking, radon reduction can prevent more lung cancer cases at the population level than in a country with minimal smoking, even if the average radon is similar.

So why do thresholds differ? Because countries are balancing multiple realities at once:

1) Risk reduction vs feasibility. A lower reference level (like 100 Bq/m³) reduces risk more, but it also means more buildings exceed the level, and the country needs the infrastructure to test and mitigate at scale.

2) Building stock and climate. Cold climates with tightly closed homes for much of the year often see higher indoor radon. Some countries build with specific radon barriers as standard practice. Others do not.

3) Existing national programs. Countries with strong testing and mitigation programs can aim for more aggressive targets. Countries with limited program capacity often start with a higher level and gradually tighten.

4) Regulatory style. Some places use a “recommendation” approach. Others embed radon in building codes and workplace regulations with compliance requirements.

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Units around the world: Bq/m³ vs pCi/L

Most of the world measures radon in becquerels per cubic meter (Bq/m³). The United States commonly uses picocuries per liter (pCi/L).

The EPA states its action level as 4 pCi/L and provides the equivalent of roughly 150 Bq/m³. EPA: Action Level for Radon

A practical conversion many people use is:

  • 1 pCi/L ≈ 37 Bq/m³
  • 4 pCi/L ≈ 148 Bq/m³ (often rounded by agencies to 150 Bq/m³)

When you see a country’s guideline in Bq/m³, you can roughly divide by 37 to estimate the equivalent in pCi/L. For example:

  • 100 Bq/m³ ≈ 2.7 pCi/L
  • 200 Bq/m³ ≈ 5.4 pCi/L
  • 300 Bq/m³ ≈ 8.1 pCi/L

The number itself is important, but how it is defined is also important. Many reference levels are defined as an annual average (or a long-term average). That is why many standards recommend long-term testing to estimate typical exposure.

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Action level vs reference level vs guideline

Different words are used, and the words matter.

Action level usually means: “At or above this level, you should take action to reduce radon.” The UK uses an “Action Level” concept for homes. UKHSA recommends reducing radon levels where the annual average in a home is above 200 Bq/m³. UKradon.org: Action Level and Target Level

Reference level is widely used in international radiation protection frameworks. A reference level is not a line between safe and unsafe. It is a policy benchmark used to guide decisions and optimization. WHO’s radon handbook recommends a reference level of 100 Bq/m³ where feasible, and says the chosen level should not exceed 300 Bq/m³ where 100 is not achievable. WHO Handbook on Indoor Radon (PDF)

Guideline is often used in public health messaging. Canada uses a guideline of 200 Bq/m³ for radon, with the point that there is no risk-free level and people can choose to reduce radon below the guideline. Health Canada: Radon guideline

The shared idea is that these values are triggers for action and policy, not “if you are below it you are perfectly safe.” The CDC’s radon guidance explicitly emphasizes that there is no known safe level of radon, even while still using the EPA action framework. CDC: Radon and Your Health

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International guidance: WHO, IAEA, and the EU

If you want to understand why so many countries cluster around “100, 200, 300,” this is the reason. International bodies have published guidance that heavily influences national policy.

World Health Organization (WHO)

WHO proposes a reference level of 100 Bq/m³ to minimize health hazards due to indoor radon exposure, and states that where 100 is not achievable, the chosen level should not exceed 300 Bq/m³. WHO Handbook on Indoor Radon (PDF)

WHO also provides broad context: indoor radon levels can vary widely across buildings, and radon contributes meaningfully to lung cancer in many countries. WHO: Radon and health

International Atomic Energy Agency (IAEA)

WHO’s Global Health Observatory metadata for radon reference levels points to IAEA Basic Safety Standards and notes a maximum reference level of 300 Bq/m³ for homes and 1000 Bq/m³ for workplaces in that framework. WHO GHO metadata: reference level for dwellings

Australia’s national radiation authority (ARPANSA) uses a similar structure: 200 Bq/m³ for households and 1000 Bq/m³ for workplaces. ARPANSA: Radon exposure and health

European Union (EU)

The EU Basic Safety Standards Directive (Council Directive 2013/59/Euratom) requires Member States to establish national reference levels for indoor radon concentrations, and the reference level for the annual average activity concentration in air shall not be higher than 300 Bq/m³. EU: Council Directive 2013/59/Euratom (PDF)

Practically, this means EU countries may set lower national levels (some do), but they should not set higher than 300 for the annual average reference level used in policy and control programs. Many EU policy briefs and guidance documents reinforce this 300 Bq/m³ cap. European Code Against Cancer: radon policy brief (PDF)

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Radon thresholds by country (selected official references)

The table below focuses on residential thresholds or reference levels. Some countries also have separate workplace levels, new-construction targets, or special building categories. When those are notable and clearly documented, they are included in the notes.

Reminder: A country having a “300 Bq/m³ reference level” does not mean 299 is safe. It means the policy trigger is set at that level for remediation guidance and program design.

Country / Region Residential threshold (typical policy trigger) What it’s called Notes
United States 4 pCi/L (about 150 Bq/m³) Action Level EPA recommends fixing at 4 pCi/L or higher, and also recommends considering action between 2 and 4 pCi/L. EPA
Canada 200 Bq/m³ Guideline / reference level Health Canada describes 200 Bq/m³ as the Canadian radon guideline and notes there is no risk-free level. Health Canada
United Kingdom 200 Bq/m³ Action Level UKHSA recommends reducing radon where annual average exceeds 200 Bq/m³. A “Target Level” of 100 Bq/m³ is also often referenced as a remediation goal. UKradon.org
Ireland 200 Bq/m³ Reference Level Ireland’s EPA notes the reference level for radon is 200 Bq/m³. Ireland EPA
European Union (EU, general rule) ≤ 300 Bq/m³ (annual average) National reference level EU Member States must set national reference levels and the annual average reference level should not be higher than 300 Bq/m³. Directive 2013/59/Euratom (PDF)
Norway 100 Bq/m³ (take steps), 200 Bq/m³ (limit value) Recommended level + limit value Norway’s DSA says you should take steps above 100 Bq/m³ and radon should not exceed 200 Bq/m³. DSA Norway
Denmark 100 Bq/m³ Reference level Nordic radon management overview describes Denmark’s reference level of 100 Bq/m³ across buildings. Nordic overview (PDF)
Sweden 200 Bq/m³ Reference level Swedish Radiation Safety Authority analysis references 200 Bq/m³ as the reference level. SSM Sweden (PDF)
Finland 300 Bq/m³ (dwellings), 200 Bq/m³ (new buildings design) Reference level STUK states 300 Bq/m³ for dwellings and 200 Bq/m³ for design and construction of new buildings. STUK Finland
Switzerland 300 Bq/m³ Reference level Switzerland’s federal health authority notes a reference level of 300 Bq/m³ for annual average in regularly occupied rooms (since 2018). Switzerland BAG
Germany 300 Bq/m³ Reference value / reference level Germany references 300 Bq/m³ as the reference value used in national work. BfS Germany
France 300 Bq/m³ Reference level France’s radon management references a 300 Bq/m³ reference level for buildings. France radon action plan (PDF)
Netherlands 100 Bq/m³ Reference level Dutch nuclear safety authority notes the Netherlands considers <100 Bq/m³ acceptable as a reference level. ANVS Netherlands
Estonia 200 Bq/m³ Regulatory limit (documented in national plan) Estonian national radon action plan annex references indoor radon concentration remaining below 200 Bq/m³ in regulated contexts. Estonia radon plan annex (PDF)
Spain 300 Bq/m³ (annual average) Reference level Spain’s National Radon Action Plan describes 300 Bq/m³ as the reference level for indoor exposure situations and references a 100 Bq/m³ design target for new buildings in guidance. Spain National Radon Action Plan (PDF)
Australia 200 Bq/m³ (households) Reference level ARPANSA recommends 200 Bq/m³ for households and 1000 Bq/m³ for workplaces. ARPANSA
New Zealand No single national numeric level clearly stated on Health NZ page WHO-aligned guidance referenced Health New Zealand references WHO’s suggested 100 to 300 Bq/m³ range and notes most places in NZ are far below these levels. Health NZ: Radon
China 300 Bq/m³ (existing buildings), 100 Bq/m³ (target for new construction) National benchmark in standards Peer-reviewed summaries describe GB/T 16146-2015 benchmarks including 300 Bq/m³ action level for existing buildings and 100 Bq/m³ target for new construction. MDPI summary (2025)
South Korea 148 Bq/m³ (often cited guideline) Recommended guideline (reported in literature) Literature reports that Korea’s Ministry of Environment recommended indoor radon be less than 148 Bq/m³. Indoor radon mitigation in South Korea (PDF)

This table is intentionally conservative: it only includes countries where an official public source (or a strong, clearly referenced national document) could be found quickly and verified. Many countries have radon programs, but their residential thresholds are not always easy to locate in a single clear English-language source. In those cases, countries often default to WHO and IAEA guidance while building national capacity.

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Regional deep dive: how major regions handle radon

North America: US vs Canada and why they differ

The United States and Canada are a useful comparison because they are neighbors with similar types of geology in many places, yet they use different primary thresholds.

United States: The EPA recommends mitigation at 4 pCi/L (about 150 Bq/m³) and also recommends considering action between 2 and 4 pCi/L because there is no known safe level of exposure. EPA: Action Level for Radon The CDC echoes this approach and recommends installing a radon reduction system at or above 4 pCi/L and considering action between 2 and 4 pCi/L. CDC: Reducing Radon Levels in Your Home

Canada: Canada uses a guideline of 200 Bq/m³ and explicitly frames it as a public health guideline with the statement that there is no risk-free level, so homeowners can choose to reduce radon even below the guideline. Health Canada: Radon guideline

The difference in numbers can make people think the countries disagree about the science. They do not. The larger difference is the policy choice about where to place the primary action trigger and how aggressively to push reductions below that trigger. Both countries acknowledge risk below the trigger and encourage reductions when feasible.

Europe: why “300” shows up everywhere, plus notable exceptions

Europe is heavily shaped by EU radiation protection policy. EU Member States must establish national reference levels and the annual average reference level should not exceed 300 Bq/m³. EU Directive 2013/59/Euratom (PDF)

Because the EU uses a “not higher than 300” framework, many countries land at 300 even if they aim to reduce lower in practice. The European Code Against Cancer radon policy brief summarizes the same policy direction: a maximum recommended level of 300 Bq/m³ within the EU framework. European Code Against Cancer: policy brief (PDF)

At the same time, several European countries choose lower residential levels, typically 100 or 200. In the examples we sourced above:

Denmark uses 100 Bq/m³. Nordic overview (PDF)

Sweden uses 200 Bq/m³. SSM Sweden (PDF)

The UK uses 200 Bq/m³ as the Action Level. UKradon.org

Ireland uses 200 Bq/m³ as a reference level. Ireland EPA

The Netherlands uses a notably low reference level of 100 Bq/m³. ANVS Netherlands

So if you live in Europe, a quick mental model is: the EU pushes the region toward structured national radon plans and a maximum of 300 Bq/m³ for the national reference level, but individual countries can choose lower levels and often do.

Asia-Pacific: Australia has a clear household level, others vary widely

Australia’s national radiation authority (ARPANSA) makes the policy trigger very clear: a household reference level of 200 Bq/m³ and a workplace reference level of 1000 Bq/m³. ARPANSA: Radon exposure and health

New Zealand’s public health guidance emphasizes radon should be kept as low as possible and references WHO’s recommended range of 100 to 300 Bq/m³, while also noting NZ generally has radon levels far below those levels. Health NZ: Radon

China is an interesting case because peer-reviewed summaries of its standards describe a dual structure that looks similar to what many countries want long term: a higher action level for existing buildings and a lower design target for new buildings. A 2025 summary describes an annual average action level of 300 Bq/m³ for existing buildings and a target level of 100 Bq/m³ for new constructions in GB/T 16146-2015. MDPI: China benchmark summary (2025)

South Korea is commonly cited as using a recommended guideline of 148 Bq/m³, often aligned with the US EPA number. A referenced mitigation paper states that Korea’s Ministry of the Environment recommended indoor radon be less than 148 Bq/m³. Indoor radon mitigation in South Korea (PDF)

Japan is frequently described as having relatively low average indoor radon compared to many Western countries. Japan’s Ministry of the Environment reference material notes an average indoor radon value of about 16 Bq/m³ compared to a global average around 39 Bq/m³. Japan MOE: Indoor Radon Japan’s “threshold” framework is harder to summarize because many sources discuss radon risk and measurement, but a single widely used national residential action level is not always presented the way the US or Canada present theirs. In practice, countries in this situation often rely on WHO and IAEA guidance as they build policy and program capacity.

Other regions: many countries use WHO guidance without a widely publicized national number

In parts of Latin America, Africa, and parts of Asia, radon programs exist but are not always consumer-visible in the same way they are in the US, Canada, the UK, or the Nordics. The scientific reality does not change. Radon is present everywhere, but the attention it receives depends on geology, building practices, and national public health focus.

WHO’s radon fact sheet is often the best “starting anchor” in these regions because it explains the risk clearly and frames radon as a major lung cancer risk factor worldwide. WHO: Radon and health

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Why one country chooses 100 and another chooses 300

At first glance, it can feel arbitrary. If radon is a carcinogen, why would a country tolerate 300 when another aims for 100?

The simplest explanation is that radon policy is optimization. WHO recommends 100 Bq/m³ where feasible and says the chosen level should not exceed 300 where 100 is not possible. WHO Handbook on Indoor Radon (PDF) This is not a scientific claim that “100 is safe and 300 is safe.” It is a policy claim about what is achievable and how to reduce population risk.

Countries that choose 100 Bq/m³ often do so because:

They want a more protective benchmark that drives earlier action, and they believe testing and mitigation capacity can handle the larger number of buildings that will exceed 100. Denmark’s 100 Bq/m³ reference level is one example. Nordic overview (PDF)

Countries that choose 200 Bq/m³ often do so because:

They want a strong trigger but may be balancing program scale, costs, or the expected distribution of radon in the housing stock. Canada (200), Ireland (200), and the UK action level (200) are examples. Health Canada Ireland EPA UKradon.org

Countries that choose 300 Bq/m³ often do so because:

They are aligning with major international frameworks and EU requirements, and they may be focusing on getting testing rates up, building radon plans, and building mitigation capacity before tightening further. The EU requires national reference levels and sets an upper bound of 300 for annual average reference levels. EU Directive 2013/59/Euratom (PDF)

This is also why you will see a “dual structure” in some places: a higher trigger for existing buildings and a lower design target for new buildings. Finland and Spain clearly describe this kind of approach. STUK Finland Spain National Radon Action Plan (PDF)

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Radon “levels by country” vs thresholds: what people confuse

Many people search “radon levels by country” because they want to know which countries have the highest radon problem. But there are two very different concepts:

1) The national threshold (reference level or action level). That is what most of this article covers. These are policy triggers.

2) The typical measured radon level in homes in that country. This is a descriptive statistic about the housing stock, not a policy decision.

It is common for a country to have a low average indoor radon level while still using a low reference level, or for a country to have a higher average and use a higher reference level. They are related, but they are not the same.

Here are a few examples of “typical measured levels” to illustrate why this matters:

Australia: ARPANSA notes that based on a nationwide survey, the average concentration of radon in Australian homes is about 10 Bq/m³, and it compares that to a global average indoor value of about 40 Bq/m³. ARPANSA: Radon in homes survey

Japan: Japan’s Ministry of the Environment reference material notes an average indoor radon value of about 16 Bq/m³ compared with a global average around 39 Bq/m³. Japan MOE: Indoor Radon

Netherlands: The Dutch nuclear safety authority states that the average concentration of radon in dwellings in the Netherlands is about 21 Bq/m³. ANVS Netherlands

In contrast, a country can have low averages but still have localized hotspots where radon is high in a subset of homes. That is why many agencies emphasize testing rather than relying on national averages.

WHO reinforces this idea by describing wide variability: indoor radon can range from low levels to extremely high levels depending on building and conditions. WHO: Radon and health

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How to use this information as a homeowner or buyer

International thresholds are useful for comparison and context, but what you should do in your own home is simpler than it seems.

Step 1: Identify your country’s unit and trigger. If you are in the US you will often see pCi/L. Most other places you will see Bq/m³. The US action trigger is 4 pCi/L and the CDC echoes that. EPA CDC

Step 2: Treat the trigger as a decision point, not a safety line. Even below 4 pCi/L, EPA recommends considering action between 2 and 4, and CDC emphasizes no known safe level. EPA CDC

Step 3: Use long-term testing if you want a more “year-round” view. WHO emphasizes that radon can vary widely and reference levels are typically built around longer-term exposure concepts. WHO Handbook on Indoor Radon (PDF)

Step 4: If your result is above your country’s policy trigger, plan mitigation instead of debating the number. The physics of radon entry does not change across borders. The most common and effective method for many foundation types is active soil depressurization (sub-slab depressurization), paired with sealing major openings as a supporting step.

Step 5: If you are buying internationally, ask for a radon test as a standard due diligence step. In some countries, radon testing is common in real estate. In others, it is not. If you are relocating to a region known for granite, uranium-rich soils, or mountainous geology, consider radon testing as routine as checking moisture or mold risk.

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FAQs

Why is the US number “4 pCi/L” when many countries use “100 to 300 Bq/m³”?

It is mostly a unit difference and a policy history difference. The US commonly uses pCi/L, while most of the world uses Bq/m³. The EPA’s 4 pCi/L is roughly 150 Bq/m³. EPA WHO recommends a reference level of 100 Bq/m³ where feasible and not exceeding 300 Bq/m³ where 100 is not achievable. WHO Handbook (PDF)

Does a higher national threshold mean a country thinks radon is less dangerous?

Not necessarily. Often it reflects policy optimization, program capacity, and how many homes are expected to exceed a lower number. Most agencies emphasize that there is no risk-free level and that risk rises with exposure. CDC

If my country’s threshold is 300 Bq/m³, should I ignore 150 Bq/m³?

No. Lower radon generally means lower risk. Even in the US, EPA recommends considering action between 2 and 4 pCi/L (75 to 150 Bq/m³). EPA

Why do some countries have separate numbers for existing buildings and new buildings?

Because it is usually easier and cheaper to prevent radon in new construction than to retrofit later. Finland states a 300 Bq/m³ reference level for dwellings and a 200 Bq/m³ reference level for design and construction of new buildings. STUK Finland Spain’s national plan describes 300 Bq/m³ as the reference level and discusses a 100 Bq/m³ design target concept in guidance for new buildings. Spain plan (PDF)

Is radon only an issue in “high radon countries”?

No. Radon can be elevated in localized areas anywhere. WHO describes indoor radon as varying widely across buildings and regions. The most reliable approach is testing, not guessing based on national averages. WHO

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Sources

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