Radon Level Calculator
Radon average, unit conversion, and fix guidance from one or two home tests.
What it does
Radon is an odorless soil gas and the second cause of lung cancer after smoking, so home tests decide real fixes. EPA draws the line at 4 pCi/L while WHO references 100 Bq/m3, and one short test alone never triggers mitigation.
The tool above averages one or two tests in either unit. It returns the average, the converted value, and a fix, consider, or low verdict.
The default 5.2 plus 3.6 pCi/L averages 4.4, or 162.8 Bq/m3, which means fix the home. The metric mirror of 192.4 plus 133.2 Bq/m3 reads the same.
Bands follow EPA action guidance with CDC testing protocol behind them. Both require closed building conditions for short tests and a follow up in the same spot.
How to use
- Pick pCi/L or Bq/m3 units.
- Enter the first test result.
- Add the second test if you have one.
- Read the average first.
- Read the other unit beside it.
- Follow the verdict, then retest rules.
Formula
- test 1
- First short or long test result.
- test 2
- Second test in the same spot, optional.
- 37
- Conversion: 1 pCi/L equals 37 Bq/m3.
- 4
- EPA action level in pCi/L.
EPA display pairs round (4 reads 150, exact 148); the tool keeps exact math with 37 and the verdict uses pCi/L bands. A missing second test averages the first alone and the note demands a follow up before any mitigation.
Worked example
Example: average of two short tests
Imperial defaults: two short tests at 5.2 and 3.6 pCi/L.
- First short test: 5.2 pCi/L.
- Second short test: 3.6 pCi/L.
- Average: (5.2 + 3.6) / 2 = 4.4 pCi/L.
- Convert: 4.4 x 37 = 162.8 Bq/m3.
- Rule: 4.4 sits at or above 4, so fix the home.
- Tool shows 4.4 pCi/L, 162.8 Bq/m3, Fix the home.
Reference table
| Level | Bq/m3 shown | Meaning |
|---|---|---|
| 4 pCi/L | 150 | EPA: fix the home |
| 2 pCi/L | 75 | EPA: consider fixing |
| 1.3 pCi/L | 50 | US indoor average |
| 0.4 pCi/L | 15 | US outdoor average |
| WHO 100 Bq/m3 | 2.7 pCi/L | WHO reference |
| WHO 300 Bq/m3 | 8.1 pCi/L | WHO ceiling |
Limits
- Screening math only; pros design mitigation.
- Short tests need closed building conditions.
- Kitchens, baths, and crawl spaces mislead.
- Weather fronts distort 2 to 3 day kits.
Common mistakes
- Mitigating on a single short test.
- Testing the wrong floor or room.
- Skipping the follow up in the same spot.
- Comparing meters across brands.
- Ignoring the 2 to 4 consider band.
Try it yourself
Quick checks. Answers sit tucked under each question.
Single short test at 3.0?
Average 3 pCi/L (111 Bq/m3): consider fixing, confirm with a follow up.
Single 40 Bq/m3 test?
40 / 37 = 1.1 pCi/L: low, retest later per schedule.
Short tests at 6.0 and 2.0?
Average (6 + 2) / 2 = 4 pCi/L (148 Bq/m3): fix the home.
Questions
When does EPA say fix the home?
At or above 4 pCi/L (about 150 Bq/m3). Consider fixing between 2 and 4. No level is known safe.
How do pCi/L convert to Bq/m3?
Multiply pCi/L by 37. So 4 pCi/L is 148 exact, shown rounded as 150.
Short vs long term tests?
2 to 90 days for short kits, over 90 days for long kits. Real estate uses 48 hour minimums.
Does one high test force mitigation?
No. One short test never decides mitigation; average two shorts or run a long test first.
Where do I place the kit?
Lowest lived-in level, 20 in off the floor, away from drafts, heat, and exterior walls.
When should I retest?
Buying or selling, after renovations, after mitigation, or when rooms below grade turn lived-in.