Q: How Is Radon Measured?

A: Radon is measure in units called picocuries per liter (pCi/l), which is one trillionth of a curie. A curie is the amount of radioactivity produced by a gram of radium. The United States Environmental Protection Agency has determined 4 pCi/l to be the standard for air indoors.  Typical radon readings on natural stone countertops are a very small fraction of the allowable limits.