Interpreting Results of Radon Measurements


Initial Measurement

You can test your own home or hire a testing contractor.

  1. Your first radon measurement should be made for a few days (two days, minimum) in the lowest lived-in level of your home, with the windows kept closed, as recommended in the United States Environmental Protection Agency's (EPA's) A Citizen'’s Guide to Radon.
  2. A basement can be considered lived-in (for radon testing purposes) if it is occupied at least 7 hours per week. Otherwise, the main floor is the best place to test or do a follow-up test.*
  3. Radon test kits are available from hardware stores, through your local public health agency or a Radon Information Center for around $20, including laboratory processing.

*Note: The testing recommendations for real estate transactions or home sales can be somewhat different. Consult with the EPA’'s Home Buyer's and Seller's Guide to Radon.

Test Results

Your test results will be reported in units of pCi/L, a measure of radon concentration. Appropriate follow-up actions, based on the results of your first measurement, are: 

Result Action
First result less than 4 pCi/L: No follow-up needed. Your home has low radon levels.
First result between 4 and 8 pCi/L: Do a year-long follow-up measurement with an alpha-track detector to determine your average radon exposure. Radon levels may change with seasons, and are low when windows are open. The average radon level in occupied floors of your home determines you lung cancer risk from radon exposure.
First result above 8 pCi/L: Do a short-term or long-term follow-up to confirm the accuracy of your first result.


If follow-up measurements indicate your radon exposure is higher than 4 pCi/L (the U.S. EPA guideline), it can be significantly reduced. The higher your confirmed radon results are, the more important it is to fix your home.

  • Outdoor air has about 0.4 pCi/L, and this is the lowest achievable level in a house.
  • The average radon level in the lowest lived-in floors of homes in Wisconsin is about 1.8 pCi/L.
  • Twenty-five percent of homes in the state have radon at over 4 pCi/L in basements.
  • In some regions of the state, more than half the homes have radon at over 4 pCi/L in basements.

How Soon to Fix Your House  

High levels of radon are dangerous to you and your family. When follow-up radon measurements in occupied levels of your home are high, you should take bids on radon mitigation work by professionals included on the list of certified radon mitigation contractors. Having this work done will protect your family and it will increase the value of your house.

If results in occupied levels of your house are confirmed to be in the range of 4 to 20 pCi/L, it may reasonably take up to a year to get the work done. For confirmed results above 20 pCi/L, mitigation action should probably be more prompt. Consult one of the Wisconsin Radon Information Centers.

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Last Revised: December 16, 2014