Radon Level Risk Calculator
Assess your radon exposure risk based on measured radon levels.
Understand EPA action levels and when to mitigate radon in your home.
Radon is a naturally occurring radioactive gas produced by the decay of uranium in soil and rock. It is colorless, odorless, and tasteless, so a test is the only way to know it is there. Radon is the #2 cause of lung cancer in the United States, responsible for approximately 21,000 deaths per year.
How radon enters homes:
Radon seeps up from the ground through cracks in foundations, floor drains, and construction joints. It accumulates in enclosed spaces, especially basements and ground-floor areas with poor ventilation. Upper floors typically have lower radon levels than ground floors and basements.
Radon measurement units:
- pCi/L (picocuries per liter), used in the United States
- Bq/m³ (becquerels per cubic meter), used in Europe and internationally
- Conversion: 1 pCi/L = 37 Bq/m³
The reference numbers worth knowing
Three figures get quoted and they are not the same thing:
- 1.3 pCi/L is the average indoor level in US homes
- 2.7 pCi/L (100 Bq/m³) is the WHO reference level, the point above which the World Health Organization recommends acting
- 4.0 pCi/L (148 Bq/m³) is the EPA action level in the United States
The WHO number is lower because the two agencies weighed cost against risk differently, not because they disagree about the science. There is no threshold below which radon is harmless; the risk simply gets smaller.
| Radon Level | Guidance |
|---|---|
| Under 2 pCi/L | At or near the US average. Retest in a couple of years |
| 2–4 pCi/L | Below the EPA action level, above the WHO one. Worth a long-term test |
| 4–8 pCi/L | EPA action level. Fix the home |
| 8–20 pCi/L | Well above. Arrange mitigation rather than waiting on more tests |
| Above 20 pCi/L | Act within months rather than years |
Lifetime cancer risk estimates (smokers versus non-smokers):
Radon and smoking are a particularly dangerous combination, because the risks multiply rather than add.
| Radon Level | Lifetime Risk (never-smoker) | Lifetime Risk (smoker) |
|---|---|---|
| 2 pCi/L | 2.5 in 1,000 | 32 in 1,000 |
| 4 pCi/L | 5 in 1,000 | 62 in 1,000 |
| 8 pCi/L | 10 in 1,000 | 120 in 1,000 |
| 20 pCi/L | 36 in 1,000 | 260 in 1,000 |
These are the EPA’s published anchor points. The calculator interpolates between them rather than rounding down to whichever row you sit above, so a reading of 3.9 reports a risk near the 4 pCi/L figure rather than the 2 pCi/L one.
For a smoking household the radon number is not the biggest lever available. At 4 pCi/L the smoker risk is over twelve times the never-smoker risk at the same level, and that gap is tobacco, not radon.
Radon mitigation:
The most common solution is sub-slab depressurization (ASD): A pipe is inserted through the floor slab and a fan draws radon out from under the house before it enters the living space. Cost: typically $800–$2,500 for a professional installation. This reduces radon by 50–99% in most homes.
Testing:
- Short-term tests (2–7 days): Use a charcoal canister from a hardware store (~$15–$25)
- Long-term tests (90+ days): More accurate seasonal average
- Professional testing: $100–$300
- Test every 2 years, or after major renovations or changes in HVAC system
How we build and check this calculator
This calculator runs entirely in your browser, so the numbers you enter stay on your device. The math behind it is written by hand and tested against worked examples and standard references before the page goes live.
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