Radon Levels Explained: What Bq/m³ Means and What's Actually Safe
Your test kit comes back. The lab sends a single number. Something like “182 Bq/m³” or “417 Bq/m³” or “78 Bq/m³.”
Then nothing. No traffic-light colour. No “safe” or “unsafe” stamp. Just a number, a guideline, and a polite note to talk to a pro if you’re worried.
That’s where most Ontario homeowners get stuck. The number means something. But what?
This post walks through what radon levels actually measure, why Canada and the US use different numbers, what each reading range really means for your home, and why “safe” is the wrong word to chase.
The short version:
- Radon is measured in Bq/m³ in Canada (becquerels per cubic metre)
- Health Canada’s action level is 200 Bq/m³. The US EPA uses 150 Bq/m³ (which is 4 pCi/L). Both target the same risk.
- Under 100 is low. 100 to 200 means retest. 200 to 600 means fix it in 2 years. 600+ means fix it within a year.
- There’s no “safe” level. Risk is a sliding scale, not an on-off switch.
- Even at 100 Bq/m³ you carry some risk. The goal is “as low as you can reasonably get it.”
What does a radon level actually measure?
Bq/m³ stands for becquerels per cubic metre. One becquerel means one radioactive decay per second.
So 200 Bq/m³ means 200 radon atoms in every cubic metre of your air are breaking down every single second.
That sounds wild. But here’s the thing.
Each decay is tiny. It shoots out one alpha particle. Most of those particles never reach a person, because they only travel a few centimetres before they stop.
The harm isn’t from the radon itself. It’s from what radon turns into.
Radon decays into things called radon daughters, which are heavier and stick to dust. You breathe that dust in. Some lands deep in your lungs.
The decay continues there, right next to soft tissue.
A test kit reads the air, not the dust. But the air number tells you how much dust is being created.
Higher air number means more dust, more particles in your lungs, more risk over time.
Bq/m³ vs pCi/L: Canada vs US
Canada uses metric. The US uses imperial. Radon is no different.
| Unit | Used in | Conversion |
|---|---|---|
| Bq/m³ (becquerels per cubic metre) | Canada, most of the world | 1 Bq/m³ = 0.027 pCi/L |
| pCi/L (picocuries per litre) | United States | 1 pCi/L = 37 Bq/m³ |
So if a US guide says the action level is 4 pCi/L, that’s 148 Bq/m³ in Canadian units. Close to 150.
If you read a Canadian guide that says 200 Bq/m³, that’s 5.4 pCi/L in US units.
Quick conversion table for the most-asked levels:
| Bq/m³ (Canada) | pCi/L (US) |
|---|---|
| 100 | 2.7 |
| 150 | 4.0 |
| 200 | 5.4 |
| 400 | 10.8 |
| 600 | 16.2 |
| 1000 | 27.0 |
If you bought a US-made monitor like the original Corentium Home, check the unit setting. Some default to pCi/L. Switch it to Bq/m³ to match Canadian guidance.
Why Canada uses 200 and the US uses 150
You’ll see both numbers online. Both are real. Neither is wrong.
Canada’s guideline is 200 Bq/m³. That’s the level Health Canada recommends taking action.
The US EPA’s action level is 4 pCi/L (148 Bq/m³). That’s where they say homeowners should act.
So why the gap?
The science is the same. Both governments built their numbers from the same body of evidence on radon and lung cancer. The split is about policy, not biology.
Canada landed at 200 in 2007. Before that, our guideline was much higher (800 Bq/m³). The drop to 200 reflected newer data on long-term risk. Some Canadian experts argue we should go lower still, closer to the US number.
The US picked 4 pCi/L because that’s the lowest level their tech could reliably measure when the EPA set the guideline in the 1980s. They’ve kept it ever since.
The World Health Organization recommends 100 Bq/m³. That’s the lowest official guideline anywhere, and it’s based on pure health risk with no cost or feasibility tradeoffs.
The honest read: any level above 100 Bq/m³ carries some lifetime risk. Canada’s 200 is a practical action threshold, not a safety line.
What each radon level range actually means
Here’s the plain-English version of what your number tells you, and how fast you should act.
| Your reading | What it means | What to do | When |
|---|---|---|---|
| Under 100 Bq/m³ | Low, about average for Ontario | Retest in 5 years or after a renovation | No rush |
| 100 to 200 Bq/m³ | Elevated but below the guideline | Retest with a long-term (91 day) kit to confirm | Within a year |
| 200 to 600 Bq/m³ | Above Health Canada’s guideline | Plan to mitigate | Within 2 years |
| 600 to 1000 Bq/m³ | High | Mitigate, and move kids’ bedrooms out of the basement in the meantime | Within 1 year |
| Over 1000 Bq/m³ | Very high | Mitigate as soon as you can | Within 6 months |
Two things to know about this table.
First, it comes from Health Canada’s measurement guide.
Second, your single test number isn’t the whole story. Short-term tests (3 to 7 days) bounce around with weather, ventilation, and the season. A long-term test (91 days or more) gives you a better picture of your true yearly average.
If your short-term reading lands between 100 and 200, follow up with a long-term kit before you decide anything.
Bold answer: at 200 Bq/m³ and above, plan to fix it. Below 200, you have time. Below 100, you can mostly forget about it for five years.
Why “safe” is the wrong word
A lot of homeowners ask, “is my level safe?”
The right answer is harder than yes or no.
Radon risk doesn’t have a floor. Even at very low levels, every breath you take carries a small chance of damaging a lung cell. The math is just so small that we round it to zero.
The Canadian Cancer Society calls radon the leading cause of lung cancer in people who’ve never smoked.
Health Canada and the EPA both phrase the goal the same way: get your level “as low as reasonably achievable.” That’s the official policy in plain English.
What this means for you:
- Below 100 Bq/m³ is the realistic floor for most Canadian homes
- 100 to 200 is where many homes land naturally
- A good mitigation system targets under 100, often under 50
If your home tests at 60 Bq/m³, you don’t need to fix anything. You’re already where most mitigation systems aim. But if you tested at 180, you’re below the guideline, yet still carrying real long-term risk.
There’s no magic line. There’s just a number, a timeline, and a decision.
Why basement bedrooms change the math
The same Bq/m³ reading carries more weight if a person sleeps below grade.
Radon is heaviest in the lowest level of a home. The basement reads highest. The main floor reads about half. The second floor reads about a quarter.
A kid sleeping in a basement bedroom spends 8 to 10 hours a night breathing the highest concentration in the house. Over 18 years, that’s a serious cumulative dose.
If your basement tests at 150 Bq/m³ and that’s where a child sleeps, treat it like a 250 Bq/m³ reading in a finished main floor. Move the bedroom or mitigate, even though the number sits below the official guideline.
The Evict Radon study found that post-1980 homes test higher than older ones on average.
DIY vs hire a pro
Reading and acting on a radon level doesn’t always need a pro. Some calls do.
| Task | DIY is fine | Hire a pro |
|---|---|---|
| Buying a $35 long-term kit and reading the result | Yes | Only if you want faster turnaround |
| Converting Bq/m³ to pCi/L for a US-made monitor | Yes, use the table above | Not needed |
| Deciding if your level is “high” against the Canadian guideline | Yes, use the table above | Not needed |
| Short-term test for a real estate transaction | No, the buyer or seller won’t accept it | Yes, $99 to $399 |
| Re-test after a mitigation install to confirm it worked | Maybe (mail-in long-term) | Yes, faster and cleaner paperwork |
| Filing a Tarion warranty claim using your test number | No, Tarion requires a certified report | Yes, the report has to come from a C-NRPP measurement professional |
The honest read: a $35 mail-in kit from Take Action on Radon or a local hardware store works fine for most Ontario homeowners.
We’d rather you spend $40 with someone else and get your answer than wait six months. Once your number is in, then come back if you need help.
What to do at each level
Quick guide. Match your number to the row.
Under 100 Bq/m³
- Save your test result.
- Retest in 5 years.
- Retest right away after a basement renovation, sump install, or new flooring over the slab.
100 to 200 Bq/m³
- Order a long-term (91 day) kit to confirm the yearly average.
- If kids sleep in the basement, mitigate anyway.
- Read more about what causes radon to enter a home.
200 to 600 Bq/m³
- Get a mitigation quote. Plan the install within 2 years.
- If it’s a new build (post Feb 2021), check the Tarion warranty path. The builder may owe you the fix.
- Retest 30 days after install to confirm the drop.
600 to 1000 Bq/m³
- Get mitigation booked within a year.
- Move basement bedroom users upstairs as a stopgap.
- Open windows for 30 minutes a day until install. It helps short term, not long term.
Over 1000 Bq/m³
- Mitigation within 6 months.
- Move anyone sleeping in the basement out now.
- These readings are rare but real. Health Canada’s Cross-Canada Survey found about 0.5% of Canadian homes test in this range.
What we do at Breathe Radon Free
We’re an Ontario-based testing service, owner-led, based in Guelph and serving the Greater Toronto Area plus surrounding Southern Ontario. We follow Health Canada protocols on every test. We tell you when you don’t need to spend.
Our pricing:
- Residential test: $99 flat. 3 to 7 days, written report. (City-specific costs and timing in our Mississauga testing guide.)
- Real estate transaction test: $399. Faster turnaround for closing.
- Long-term test: $299. 91-day alpha track for the most accurate yearly picture.
- Mitigation: $2,800 to $3,800. Full system, post-mitigation verification.
- Tarion claim help: free for test customers.
If your test reads under 200, we’ll say so. If your test reads above, we’ll walk you through what the number means and what to do next.
For the bigger picture, our Ontario radon guide covers geology, statistics, and the basics in one place.
Frequently asked questions
What is a safe radon level in Canada?
There’s no fully safe level. Health Canada’s action guideline is 200 Bq/m³.
Below 100 Bq/m³ is considered low. Between 100 and 200 is elevated but not at the action threshold. Above 200 means you should plan to mitigate. The World Health Organization recommends a lower threshold of 100 Bq/m³ based on lifetime risk.
What’s the difference between Bq/m³ and pCi/L?
They’re two units for the same thing. Bq/m³ is metric, used in Canada and most of the world. pCi/L is imperial, used in the US.
To convert, multiply pCi/L by 37 to get Bq/m³. Or divide Bq/m³ by 37 to get pCi/L. The US action level of 4 pCi/L equals about 148 Bq/m³.
Is 100 Bq/m³ safe?
It’s well below Health Canada’s action guideline. Most homeowners at this level don’t mitigate. But the World Health Organization sets its target at 100 Bq/m³, which means even this level carries some long-term risk. If kids sleep in a basement that reads 100, many parents choose to mitigate anyway for peace of mind.
What does 200 Bq/m³ mean for my health?
At 200 Bq/m³, a lifetime non-smoker’s risk of radon-caused lung cancer rises to roughly 1 in 20 over a lifetime of exposure.
How accurate is a single radon test?
A short-term kit (3 to 7 days) can vary by 30 to 50 percent from your home’s true yearly average. Weather, ventilation, and the season all push the reading around. A long-term kit (91 days or more) is much closer to your real exposure. For a number you can actually trust, use a long-term kit or a continuous monitor that averages over months.
Do radon levels go up in winter?
Yes. Closed windows plus a running furnace pull more soil gas into the home through cracks and floor drains. A winter short-term test can read 30 to 50 percent higher than a summer one in the same home. That’s why Health Canada recommends testing during the colder months (October to March) for the most conservative reading.
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Authored by the Breathe Radon Free Team. Every claim is backed by a primary source. Full bibliography at /sources.
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